diff --git a/app/api/watermark-remove/route.ts b/app/api/watermark-remove/route.ts
index ea477d911..78b51cab4 100644
--- a/app/api/watermark-remove/route.ts
+++ b/app/api/watermark-remove/route.ts
@@ -319,16 +319,24 @@ export async function POST(request: NextRequest) {
     if (image_url.startsWith("data:")) {
       console.log("[WatermarkRemove] 检测到base64格式，上传到S3...");
       try {
-        // 解析 base64 data URL
-        const matches = image_url.match(/^data:image\/(\w+);base64,(.+)$/);
-        if (!matches) {
+        // 避免对超长 base64 使用正则，直接按 data URL 头部拆分
+        const commaIndex = image_url.indexOf(",");
+        if (commaIndex <= 0) {
           return NextResponse.json(
             { error: "无效的图片格式" },
             { status: 400 }
           );
         }
-        const ext = matches[1] === "jpeg" ? "jpg" : matches[1];
-        const base64Data = matches[2];
+        const header = image_url.slice(0, commaIndex);
+        const base64Data = image_url.slice(commaIndex + 1);
+        const headerMatch = header.match(/^data:image\/([a-zA-Z0-9.+-]+);base64$/i);
+        if (!headerMatch || !base64Data) {
+          return NextResponse.json(
+            { error: "无效的图片格式" },
+            { status: 400 }
+          );
+        }
+        const ext = headerMatch[1].toLowerCase() === "jpeg" ? "jpg" : headerMatch[1].toLowerCase();
         const buffer = Buffer.from(base64Data, "base64");
         
         // 上传到 S3