Abstract: To determine the distance between the middle cerebral artery （MCA） and the origin of internal artery （ICA） in rats and observe the relationships of the inserted thread length to the MCA origin and to the successful model-making rate.：A thread occlusion method was used to make a MCAO model. Artery perfusion color casting was performed，and the distance between the origin of MCA and the origin of ICA was measured in the inserted thread length group. The cerebral infarct area was analysised and the cerebral infarct volume was calculated by computer image processing in the infarct volume group. The result showed that the distance between MCA and ICA ranged from 1.55cm to 1.65 cm. On the condition that the length of the inserted nylon thread was less than or equal to 1.60 cm, the successful model-making rate was 28.57%） if the length was more than 1.60cm , the successful rate was 83.33% （P＜0.05）. Conclusion：If we use a thread occlusion method to make a rat MCAO model, the length of inserted nylon thread must be no less than 1.65cm.