diff --git a/apps/web/src/api/generation/cover.ts b/apps/web/src/api/generation/cover.ts
index 7c1d98bf6..948d4b3df 100644
--- a/apps/web/src/api/generation/cover.ts
+++ b/apps/web/src/api/generation/cover.ts
@@ -51,12 +51,18 @@ export interface GenerateCoverResponse {
 
 /** AI 生成封面 — 从最终成片中抽帧（MediaKit 选帧） */
 export async function generateCover(
-  templateId: string,
+  templateId: string | undefined | null,
   data: GenerateCoverRequest,
 ): Promise<GenerateCoverResponse> {
+  // templateId 为空时不传该参数，让后端使用默认模板配置
+  // （前端此前用 "default" 作为占位符，该 id 不存在于后端模板库会 404）
+  const params: Record<string, string> = {}
+  if (templateId && templateId !== "default") {
+    params.template_id = templateId
+  }
   const response = await apiClient.post<GenerateCoverResponse>("/generation/generate-cover", data, {
     timeout: 300000,
-    params: { template_id: templateId },
+    params,
   })
   return response.data
 }
diff --git a/apps/web/src/components/cover/useSharedCover.ts b/apps/web/src/components/cover/useSharedCover.ts
index 4db30d162..574c5bddd 100644
--- a/apps/web/src/components/cover/useSharedCover.ts
+++ b/apps/web/src/components/cover/useSharedCover.ts
@@ -85,6 +85,13 @@ export function useSharedCover(opts: UseSharedCoverOptions): UseSharedCoverRetur
         config: t.config,
       }))
       setTemplates(list)
+      // 若当前选中 "default"（初始占位），自动解析为第一个系统模板的真实 id
+      // （"default" 不是后端真实模板 id，传过去会 404）
+      setSelectedTemplateId((prev) => {
+        if (prev !== "default") return prev
+        const firstSys = list.find((t) => t.is_system)
+        return firstSys?.id || list[0]?.id || "default"
+      })
     } catch (err) {
       const axiosErr = err as {
         response?: {
@@ -112,6 +119,11 @@ export function useSharedCover(opts: UseSharedCoverOptions): UseSharedCoverRetur
     }
   }, [])
 
+  useEffect(() => {
+    // 挂载时拉一次模板列表，用于把 "default" 占位符解析成真实模板 id
+    void reloadTemplates()
+  }, [reloadTemplates])
+
   useEffect(() => {
     if (showCoverSettings) {
       void reloadTemplates()
@@ -193,7 +205,12 @@ export function useSharedCover(opts: UseSharedCoverOptions): UseSharedCoverRetur
         await deleteCoverTemplate(id)
         setTemplates((prev) => prev.filter((t) => t.id !== id))
         if (selectedTemplateId === id) {
-          setSelectedTemplateId("default")
+          // 删除后选中第一个系统模板作为兜底，避免 magic string "default" 传后端 404
+          setTemplates((prevAfter) => {
+            const firstSys = prevAfter.find((t) => t.is_system)
+            setSelectedTemplateId(firstSys?.id || prevAfter[0]?.id || "")
+            return prevAfter
+          })
         }
       } catch (err) {
         const axiosErr = err as {
@@ -231,7 +248,8 @@ export function useSharedCover(opts: UseSharedCoverOptions): UseSharedCoverRetur
     }
     setGenerating(true)
     try {
-      const url = await generateFn(selectedTemplateId || "default")
+      const tplId = selectedTemplateId && selectedTemplateId !== "default" ? selectedTemplateId : ""
+      const url = await generateFn(tplId)
       if (!url) {
         message.warning("封面生成未返回图片，请重试")
       }
@@ -266,7 +284,7 @@ export function useSharedCover(opts: UseSharedCoverOptions): UseSharedCoverRetur
 
   const selectedTemplateName =
     templates.find((t) => t.id === selectedTemplateId)?.name ||
-    (selectedTemplateId === "default" ? "默认模板" : "自定义")
+    (selectedTemplateId === "default" || !selectedTemplateId ? "默认模板" : "自定义")
 
   return {
     templates,
diff --git a/apps/web/src/pages/generate/components/Step6CoverSettings.tsx b/apps/web/src/pages/generate/components/Step6CoverSettings.tsx
index a94c0275e..2a24287ca 100755
--- a/apps/web/src/pages/generate/components/Step6CoverSettings.tsx
+++ b/apps/web/src/pages/generate/components/Step6CoverSettings.tsx
@@ -186,7 +186,7 @@ const Step6CoverSettings: React.FC<Step6CoverSettingsProps> = (props) => {
    * 透传给 useBatchCovers，由其在 generateOne/generateAll 中发给后端。
    */
   const batchCovers = useBatchCovers({
-    selectedTemplate: shared.selectedTemplateId || "default",
+    selectedTemplate: shared.selectedTemplateId,
     generatedVideos: props.generatedVideos,
     titles: batchTitles,
     titleStyle: {
diff --git a/apps/web/src/pages/generate/components/cover-settings/CoverSettingsModal.tsx b/apps/web/src/pages/generate/components/cover-settings/CoverSettingsModal.tsx
index 37923b6be..786a5ed5b 100644
--- a/apps/web/src/pages/generate/components/cover-settings/CoverSettingsModal.tsx
+++ b/apps/web/src/pages/generate/components/cover-settings/CoverSettingsModal.tsx
@@ -1,4 +1,4 @@
-import React from "react"
+import React, { useMemo, useState } from "react"
 import type { CoverTemplate } from "../../types/cover"
 import Modal from "@/components/ui/Modal"
 import Button from "@/components/ui/Button"
@@ -17,15 +17,58 @@ interface CoverSettingsModalProps {
   onCreateNew: () => void
 }
 
-const GRADIENT_MAP: Record<string, string> = {
-  default: "linear-gradient(135deg, #e0e0e0, #c0c0c0)",
-  "bold-red": "linear-gradient(135deg, #ef4444, #b91c1c)",
-  "elegant-black": "linear-gradient(135deg, #374151, #111827)",
-  "gradient-blue": "linear-gradient(135deg, #3b82f6, #1d4ed8)",
-  "gradient-purple": "linear-gradient(135deg, #8b5cf6, #6d28d9)",
-  "warm-orange": "linear-gradient(135deg, #f97316, #ea580c)",
-  "fresh-green": "linear-gradient(135deg, #22c55e, #15803d)",
-  "tech-blue": "linear-gradient(135deg, #06b6d4, #0e7490)",
+/** 模板缩略图：优先渲染 thumbnail_url；加载失败/无图时展示占位 */
+const TemplateThumb: React.FC<{ tpl: CoverTemplate; isSelected: boolean }> = ({
+  tpl,
+  isSelected,
+}) => {
+  const [errored, setErrored] = useState(false)
+  const url = tpl.thumbnail_url && !errored ? tpl.thumbnail_url : ""
+  // 随机柔和渐变做占位，保证卡片不会灰成一片
+  const placeholderBg = useMemo(() => {
+    const palettes = [
+      ["#e0e0e0", "#c0c0c0"],
+      ["#ef4444", "#b91c1c"],
+      ["#374151", "#111827"],
+      ["#3b82f6", "#1d4ed8"],
+      ["#8b5cf6", "#6d28d9"],
+      ["#f97316", "#ea580c"],
+      ["#22c55e", "#15803d"],
+      ["#06b6d4", "#0e7490"],
+    ]
+    let h = 0
+    for (const ch of tpl.id || tpl.name || "") h = (h * 31 + ch.charCodeAt(0)) >>> 0
+    const [a, b] = palettes[h % palettes.length]
+    return `linear-gradient(135deg, ${a}, ${b})`
+  }, [tpl.id, tpl.name])
+
+  return (
+    <div
+      className="xx-cover-template-thumb"
+      style={{
+        background: url ? "#000" : placeholderBg,
+        position: "relative",
+        overflow: "hidden",
+      }}
+    >
+      {isSelected && <span className="xx-cover-template-check">✓</span>}
+      {url ? (
+        <img
+          src={url}
+          alt={tpl.name}
+          onError={() => setErrored(true)}
+          style={{
+            width: "100%",
+            height: "100%",
+            objectFit: "cover",
+            display: "block",
+          }}
+        />
+      ) : (
+        <span style={{ fontSize: 28, opacity: 0.5 }}>🖼️</span>
+      )}
+    </div>
+  )
 }
 
 const CoverSettingsModal: React.FC<CoverSettingsModalProps> = ({
@@ -97,13 +140,7 @@ const CoverSettingsModal: React.FC<CoverSettingsModalProps> = ({
                 className={`xx-cover-template-card${isSelected ? " selected" : ""}`}
                 onClick={() => onSelectTemplate(tpl.id)}
               >
-                <div
-                  className="xx-cover-template-thumb"
-                  style={{ background: GRADIENT_MAP[tpl.id] || GRADIENT_MAP.default }}
-                >
-                  {isSelected && <span className="xx-cover-template-check">✓</span>}
-                  🖼️
-                </div>
+                <TemplateThumb tpl={tpl} isSelected={isSelected} />
                 <div className="xx-cover-template-info">
                   <div className="xx-cover-template-name">
                     {tpl.name}
diff --git a/apps/web/src/pages/generate/hooks/useBatchCovers.ts b/apps/web/src/pages/generate/hooks/useBatchCovers.ts
index 859c893c0..80d607a01 100644
--- a/apps/web/src/pages/generate/hooks/useBatchCovers.ts
+++ b/apps/web/src/pages/generate/hooks/useBatchCovers.ts
@@ -107,54 +107,57 @@ export function useBatchCovers({
       addBusy(index)
       try {
         const titleText = titles[index] || ""
-        const response = await generateCover(selectedTemplate || "default", {
-          generated_video_id: target.id,
-          video_url: target.file_url || target.download_url || "",
-          cover_type: "ai_frame",
-          ...(titleText
-            ? {
-                title_config: {
-                  text: titleText,
-                  font: titleStyle.font,
-                  font_size: titleStyle.size,
-                  font_color: titleStyle.color,
-                  position: titleStyle.position,
-                  bold: titleStyle.bold,
-                  italic: titleStyle.italic,
-                  stroke: titleStyle.stroke
-                    ? {
-                        enabled: true,
-                        width: titleStyle.strokeWidth ?? 4,
-                        color: titleStyle.strokeColor ?? "#000000",
-                      }
-                    : { enabled: false },
-                  shadow: titleStyle.shadow
-                    ? {
-                        enabled: true,
-                        offset_x: titleStyle.shadowOffsetX ?? 2,
-                        offset_y: titleStyle.shadowOffsetY ?? 2,
-                        blur: titleStyle.shadowBlur ?? 4,
-                        color: titleStyle.shadowColor ?? "rgba(0,0,0,0.8)",
-                      }
-                    : { enabled: false },
-                  line_height: titleStyle.lineHeight ?? 1.2,
-                  margin_top: titleStyle.marginTop ?? 24,
-                  max_chars_per_line: titleStyle.maxCharsPerLine ?? 0,
-                  background: titleStyle.bgEnabled
-                    ? {
-                        enabled: true,
-                        color: titleStyle.bgColor,
-                        padding: titleStyle.bgPadding,
-                        radius: titleStyle.bgRadius,
-                      }
-                    : { enabled: false },
-                  line_overrides: (titleStyle.lineOverrides ?? []) as Array<
-                    Record<string, unknown>
-                  >,
-                },
-              }
-            : {}),
-        })
+        const response = await generateCover(
+          selectedTemplate && selectedTemplate !== "default" ? selectedTemplate : undefined,
+          {
+            generated_video_id: target.id,
+            video_url: target.file_url || target.download_url || "",
+            cover_type: "ai_frame",
+            ...(titleText
+              ? {
+                  title_config: {
+                    text: titleText,
+                    font: titleStyle.font,
+                    font_size: titleStyle.size,
+                    font_color: titleStyle.color,
+                    position: titleStyle.position,
+                    bold: titleStyle.bold,
+                    italic: titleStyle.italic,
+                    stroke: titleStyle.stroke
+                      ? {
+                          enabled: true,
+                          width: titleStyle.strokeWidth ?? 4,
+                          color: titleStyle.strokeColor ?? "#000000",
+                        }
+                      : { enabled: false },
+                    shadow: titleStyle.shadow
+                      ? {
+                          enabled: true,
+                          offset_x: titleStyle.shadowOffsetX ?? 2,
+                          offset_y: titleStyle.shadowOffsetY ?? 2,
+                          blur: titleStyle.shadowBlur ?? 4,
+                          color: titleStyle.shadowColor ?? "rgba(0,0,0,0.8)",
+                        }
+                      : { enabled: false },
+                    line_height: titleStyle.lineHeight ?? 1.2,
+                    margin_top: titleStyle.marginTop ?? 24,
+                    max_chars_per_line: titleStyle.maxCharsPerLine ?? 0,
+                    background: titleStyle.bgEnabled
+                      ? {
+                          enabled: true,
+                          color: titleStyle.bgColor,
+                          padding: titleStyle.bgPadding,
+                          radius: titleStyle.bgRadius,
+                        }
+                      : { enabled: false },
+                    line_overrides: (titleStyle.lineOverrides ?? []) as Array<
+                      Record<string, unknown>
+                    >,
+                  },
+                }
+              : {}),
+          },
+        )
         const url = response.cover?.image_url || response.cover?.thumbnail_url || ""
         if (url) {
           patchCover(index, url)