diff --git a/opensora/datasets/datasets.py b/opensora/datasets/datasets.py
index 4c2b3164..0fb94c42 100644
--- a/opensora/datasets/datasets.py
+++ b/opensora/datasets/datasets.py
@@ -131,7 +131,7 @@ def getitem(self, index):
         path = sample["path"]
         text = sample["text"]
         file_type = self.get_type(path)
-        ar = width / height
+        ar = height / width
 
         video_fps = 24  # default fps
         if file_type == "video":