diff --git a/OpenAttack/metric/sim_cos.py b/OpenAttack/metric/sim_cos.py
index f15a8e6b..f60e5fb7 100644
--- a/OpenAttack/metric/sim_cos.py
+++ b/OpenAttack/metric/sim_cos.py
@@ -1,10 +1,11 @@
-from sentence_transformers import SentenceTransformer, util
+
 class Sim_Cos():
     def __init__(self):
+        from sentence_transformers import SentenceTransformer
         from ..data_manager import DataManager
         self.model = SentenceTransformer(DataManager.load("AttackAssist.SentenceTransformer"), device='cuda')
     def __call__(self, sen1, sen2):
-
+        from sentence_transformers import util
         emb1,emb2 = self.model.encode([sen1,sen2],show_progress_bar=False)
         cos_sim = util.pytorch_cos_sim(emb1, emb2)
         return cos_sim.cpu().numpy()[0][0]