diff --git a/HLS_SuPER/HLS_PER.py b/HLS_SuPER/HLS_PER.py
index feb02ab..bde9684 100644
--- a/HLS_SuPER/HLS_PER.py
+++ b/HLS_SuPER/HLS_PER.py
@@ -55,6 +55,9 @@ def open_hls(
     da_org = rxr.open_rasterio(url, chunks=chunk_size, mask_and_scale=False).squeeze(
         "band", drop=True
     )
+    # (Add) 若未获取到数据, 则返回 None
+    if da_org is None:
+        return None
     # (Add) 复制源数据进行后续操作, 以便最后复制源数据属性信息
     da = da_org.copy()
 
@@ -215,13 +218,24 @@ def process_granule(
             if not os.path.isfile(output_file):
                 # Open Asset
                 da = open_hls(url, roi, clip, scale, chunk_size)
+                # (Add) 若返回的da为None, 则表示该url对应的文件不存在/无法访问, 再次尝试无果后将会跳过
+                if da is None:
+                    logging.warning(
+                        f"Asset {url} not found in {output_dir}. Try again."
+                    )
+                    # 再次尝试下载
+                    da = open_hls(url, roi, clip, scale, chunk_size)
+                    if da is None:
+                        logging.warning(f"Asset {url} still not found. Skipping.")
+                        continue
 
                 # Apply Quality Mask if Desired
                 if quality_filter:
                     da = da.where(~qa_mask)
 
                 # Write Output
-                if "FMASK" in output_name:
+                if "FMASK" in output_name and not quality_filter:
+                    # (Add) 若 quality_filter=False, 则需要将质量层文件另外保存
                     da.rio.to_raster(raster_path=output_file, driver="COG")
                 else:
                     # (Add) 固定输出为 float32 类型, 否则会默认 float64 类型