diff --git a/src/main/java/com/genersoft/iot/vmp/aiot/service/impl/AiScreenshotServiceImpl.java b/src/main/java/com/genersoft/iot/vmp/aiot/service/impl/AiScreenshotServiceImpl.java
index 4a46aa391..2c22fcc9c 100644
--- a/src/main/java/com/genersoft/iot/vmp/aiot/service/impl/AiScreenshotServiceImpl.java
+++ b/src/main/java/com/genersoft/iot/vmp/aiot/service/impl/AiScreenshotServiceImpl.java
@@ -33,8 +33,8 @@ public class AiScreenshotServiceImpl implements IAiScreenshotService {
     private static final String SNAP_CACHE_KEY_PREFIX = "snap:cache:";
     private static final String SNAP_RESULT_KEY_PREFIX = "snap:result:";
 
-    /** 缓存 TTL（秒） */
-    private static final long SNAP_CACHE_TTL = 300;
+    /** 缓存 TTL（秒）— 与 COS presigned URL 有效期(1小时)匹配，设为 30 分钟 */
+    private static final long SNAP_CACHE_TTL = 1800;
     /** 最大等待时间（秒） */
     private static final long MAX_WAIT_SECONDS = 15;
     /** 降级 Redis 结果 TTL（秒） */
@@ -80,6 +80,21 @@ public class AiScreenshotServiceImpl implements IAiScreenshotService {
                     log.warn("[AI截图] 缓存解析失败: {}", e.getMessage());
                 }
             }
+
+            // 1.5 Redis 缓存未命中 → 从 DB 读取持久化的 cos_key，生成新 presigned URL
+            // 这样 Redis 过期后不需要重新触发 Edge 截图
+            String cosKey = snapshotMapper.getCosKey(cameraCode);
+            if (cosKey != null && cosUtil.isAvailable()) {
+                String presignedUrl = cosUtil.generatePresignedUrl(cosKey);
+                if (presignedUrl != null) {
+                    writeCache(cameraCode, presignedUrl);
+                    result.put("status", "ok");
+                    result.put("url", presignedUrl);
+                    result.put("cached", true);
+                    log.info("[AI截图] DB兜底命中: cameraCode={}, cosKey={}", cameraCode, cosKey);
+                    return result;
+                }
+            }
         }
 
         // 2. 生成 request_id 和 COS 路径