Objective To determine the relationship between thyroid hormones levels and cardiac function and structure in type 2 diabetes mellitus (T2DM) patients with normal thyroid function. Methods Totally 526 cases of T2DM patients with normal thyroid function were enrolled, and their information including gender, age, course of disease, blood pressure, blood lipids, liver and kidney functions, and thyroid function were collected; Color diagnostic ultrasound equipment was used to analyze the structure and function of the heart. Results Compared with the male group, the indexes including total cholesterol(TC), high density lipoproteincholesterol (HDL-C), low density lipoproteincholesterol(LDL-C), left ventricular ejection fraction(LVEF）, and thyroid stimulating hormone(TSH) were significantly higher in the female group, while the indexes including height, weight, hemoglobin（Hb）, blood urea nitrogen（BUN）, creatinine(Cr), uric acid(UA), left atrial diameter (LAD), interventricular septum thickness(IVST), left ventricular end diastolic diameter (LVEDD), left ventricular posteriorwall thickness(LVPWT), left ventricular end systolic diameter(LVESD), aortic root diameter(AORD), free triiodothyronine(FT₃), and free thyroxine(FT₄) were significantly lower in the female group (all P<0.05). Correlation analysis showed that FT₃ was positively correlated with LVPWT, LVESD and AORD in the general population (all P<0.05 ). In the male group, TSH was positively correlated with LVESD; in female group, FT₃ was positively correlated with LAD and LVESD, and FT₄ was negatively correlated with LVEF(P<0.05). Multiple linear regression analysis showed that for female patients, FT₃ was an independent fact of LVESD, as the other independents factors, which were age, duration of diabetes, body mass index (BMI), glycosylated hemoglobin, diastolic blood pressure and systolic blood pressure. Conclusions For T2DM patients with normal thyroid function, as the increase of circulating thyroid hormones, LVPWT and LVESD increase. Multiple regression analysis showed that FT₃ was independently and positively correlated with cardiac structure in female patients. These results indicate that thyroid hormone levels in patients with T2DM might have an impact on the heart changes even if they are within the normal range.