diff --git a/internal/controller/post_controller.go b/internal/controller/post_controller.go
index 3e83233..8a8eb68 100644
--- a/internal/controller/post_controller.go
+++ b/internal/controller/post_controller.go
@@ -416,22 +416,19 @@ func (ctrl *PostController) UploadImage(c *gin.Context) {
 	isGIF := ext == ".gif"
 
 	// 强制解码验证文件是否为有效图片（防伪扩展名、图片投毒），验证失败直接拒绝
-	// JPEG/PNG：解码后顺便做 WebP 压缩
+	// JPEG/PNG：解码后做 WebP 压缩（二分查找质量，目标 ≤ 原文件大小）
 	if isJPEGPNG {
 		img, _, err := image.Decode(bytes.NewReader(data))
 		if err != nil {
 			common.Error(c, http.StatusBadRequest, "图片格式无效，请上传有效的图片文件")
 			return
 		}
-		// WebP 压缩存储（保留原尺寸，quality 80）
-		var buf bytes.Buffer
-		if err := webp.Encode(&buf, img, &webp.Options{Quality: 80}); err == nil {
-			if buf.Len() > 0 && buf.Len() < len(data) {
-				filename := fmt.Sprintf("%d_%d.webp", uid, ts)
-				savePath = filepath.Join(storageDir, filename)
-				if err := os.WriteFile(savePath, buf.Bytes(), 0644); err == nil {
-					url = "/uploads/posts/" + filename
-				}
+		webpData := encodeWebPBinary(img, len(data))
+		if webpData != nil && len(webpData) < len(data) {
+			filename := fmt.Sprintf("%d_%d.webp", uid, ts)
+			savePath = filepath.Join(storageDir, filename)
+			if err := os.WriteFile(savePath, webpData, 0644); err == nil {
+				url = "/uploads/posts/" + filename
 			}
 		}
 	}
@@ -452,7 +449,7 @@ func (ctrl *PostController) UploadImage(c *gin.Context) {
 		}
 	}
 
-	// 原格式存储（WebP / GIF / 转换后反而更大）
+	// 原格式存储（GIF / 已有 WebP / 二分压缩仍超原文件大小）
 	if savePath == "" {
 		filename := fmt.Sprintf("%d_%d%s", uid, ts, ext)
 		savePath = filepath.Join(storageDir, filename)
@@ -474,3 +471,33 @@ func (ctrl *PostController) applyShortcode(post *model.Post) {
 	}
 }
 
+// encodeWebPBinary 二分查找 WebP 质量，找 ≤ targetBytes 的最高质量（quality 50~80）
+// 返回 nil 表示最低质量仍超限，应由调用方回退原格式
+func encodeWebPBinary(img image.Image, targetBytes int) []byte {
+	var buf bytes.Buffer
+	if err := webp.Encode(&buf, img, &webp.Options{Quality: 80}); err != nil {
+		return nil
+	}
+	if buf.Len() <= targetBytes {
+		return buf.Bytes()
+	}
+
+	low, high := 50, 80
+	var best []byte
+	for low <= high {
+		mid := (low + high) / 2
+		buf.Reset()
+		if err := webp.Encode(&buf, img, &webp.Options{Quality: float32(mid)}); err != nil {
+			return nil
+		}
+		if buf.Len() <= targetBytes {
+			best = make([]byte, buf.Len())
+			copy(best, buf.Bytes())
+			low = mid + 1
+		} else {
+			high = mid - 1
+		}
+	}
+	return best
+}
+