Objective To investigate the relationship between the insulin sensitivity and the thyroid hormone levels in the pa‐tients with type 2 diabetes mellitus(T2DM ) to provide reference for the clinical diagnosis and treatment .Methods 86 patients with T2DM were selected as the observation group and contemporaneous 72 healthy persons were selected as the control group .All pa‐tients were detected the fasting plasma glucose (FPG) ,oral glucose tolerance test postprandial 2 h blood glucose (2 h PG) and thy‐roid hormons including free tetraiodothyronine (FT4) ,free triiodothyronine (FT3) and thyroid stimulating hormone (TSH) .The insulin sensitivity index (ISI) was calculated .The relationship between the insulin sensitivity with thyroid hormone levels was ana‐lyzed .Results FT3 ,FT4 ,FT3 /FT4 ,HOMA‐IR and ISI in the observation group were (4 .82 ± 1 .13) pmol /L ,(13 .12 ± 4 .36) pmol /L 0 .39 ± 0 .08 ,2 .94 ± 0 .37 and -5 .18 ± 0 .82 respectively ,which showing statistically significant differences compared with those in the control group(P<0 .05) ,the TSH level in the observation group was (2 .51 ± 1 .03) mU /L ,the difference between the two groups was not statistically significant (P> 0 .05);HOMA‐IR and FT3 had a negative correlation (r= -0 .543 ,P=0 .000) ,HOMA‐IR and FT4 had a positive correlation (r=0 .611 ,P=0 .000) ,ISI was positively correlated with FT3 (r=0 .551 ,P=0 .001) and negatively correlated with FT 4 (r= -0 .599 ,P=0 .000) .Conclusion The thyroid hormone levels are closely corre‐lated with the insulin sensitivity ,the thyroid hormone levels may be the partial pathological causes of T 2DM pathogenesis .