Objective To explore the relationship between FT3 level and intracranial and extracranial atherosclerotic stenosis in patients with acute cerebral infarction. Methods A total of 148 cases of acute cerebral infarction were selected as the experimental group， and 97 cases of non-acute cerebral infarction admitted in the same period were treated as the control group. The general clinical features of the two groups were compared， and the variables（ P＜0.05） were included in the regression analysis. According to the location and degree of arteriosclerosis， the experimental group was divided into subgroups to compare the level of FT3. Results The level of FT3 and TSH in patients with acute cerebral infarction was significantly lower than that in the control group（ P＜0.05）. The result of Logistic regression analysis showed that FT3 was the protective factor of acute cerebral infarction（ OR=0.060， 95%CI=0.019-0.191， P＜0.001）， and an independent protective factor for arteriosclerosis in FT3 acute cerebral infarction（ OR=0.049，95%CI=0.015-0.157，P＜0.001）. There was no significant difference in the location and degree of intracranial arteriosclerosis and the degree of arteriosclerosis between the carotid arteries（ P＞0.05）. The level of FT3 showed a decrease trend， as the degree of carotid stenosis increased. Conclusions The level of FT3 in patients with acute cerebral infarction decreases， and FT3 is a protective factor for acute cerebral infarction. The level of FT3 is not related to the location and degree of intracranial stenosis and the degree of carotid artery stenosis in acute cerebral infarction.