Objective: To investigate the correlation between serum thyroid hormone level and free triiodothyronine( FT3) /free thyroxine (FT4) ratio and non-alcoholic fatty liver disease (NAFLD) in type-2 diabetes mellitus (T2DM) patients with normal thyroid function. Methods: Clinical data of 1 018 patients with T2DM admitted to the Department of Endocrinology, The Third Affiliated Hospital of Anhui Medical University from January 2010 to December 2016 were collected. The patients were divided into a T2DM group and a NAFLD group with or without NAFLD, and into the FT3 <3.70, 3.70–4.19 and >4.19 pmol/L groups according to the FT3 level. General information and biochemical indicators were compared in each group, and FT3, FT3/FT4 ratio and the prevalence of NAFLD were analyzed. Spearman correlation analysis was used to analyze the correlation between NAFLD and each indicator, and the ROC curve was used to analyze the FT3/FT4 ratio to predict the risk of NAFLD. Results: Compared with the T2DM group, the patients in the NAFLD group were younger, had a shorter course of disease, with higher BMI, systolic blood pressure, ALT, AST, GGT, SUA, TG, TC, FT3, FT3/FT4, and FCP and lower HDL-C (P<0.05); with the improvement of FT3 level, ALT, GGT, TG, TC, FCP also increased significantly, while SCR decreased (P<0.05). After grouping according to FT3 level and FT3/FT4 value, the prevalence of NAFLD increased significantly with the increase of FT3 level and FT3/FT4 ratio. Spearman correlation analysis showed that NAFLD was positively correlated with BMI, ALT, AST, GGT, SUA, TC, TG, HDL-C, FT3/FT4, FT3 and FCP (P<0.01), and negatively correlated with age and disease course (P<0.05). Further ROC curve analysis revealed that FT3/FT4 ratio could be used as a serological indicator to predict the risk of NAFLD. Conclusion: The serum FT3 level and FT3/FT4 ratio in T2DM patients with normal thyroid function are independently and positively correlated with the risk of NAFLD, and the FT3/FT4 ratio may effectively predict the risk of NAFLD.