Objective: To explore the related influencing factors of carotid atherosclerosis (AS) plaque formation and stability in the elderly patients with type 2 diabetes mellitus (T2DM), and to provide scientific evidence for early prevention and treatment. Methods: A total of 262 elderly patients with T2DM were selected. According to the results of carotid artery color Doppler ultrasound, they were divided into a normal group, an AS group, a stable plaque group and an unstable plaque group. The differences of clinical data and biochemical indicators of patients were compared between the 4 groups; univariate analysis and logistic regression analysis were used to screen the related influencing factors of carotid AS plaque formation and stability of the elderly T2DM patients. Results: The analysis showed that the disease course, serum fasting blood glucose (FBG), hemoglobin A1c (HbA1c), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), total bilirubin (TBIL), direct bilirubin (DBIL), free triiodothyronine (FT3), free thyroxine (FT4), 25(OH)VD has significant differences among the normal group, the AS group and the plaque group (P<0.05). The significant differences in the levels of the disease course, serum HbA1c, HDL-C, LDL-C and 25(OH)VD in the stable plaque group and the unstable plaque group (P<0.05). The logistic regression analysis showed that the long disease course, high FBG and LDL-C were the risk factors of plaque formation, high FT3, HDL-C, TBIL, 25(OH)VD were protective factors of plaque formation. Conclusion: The decrease of serum FT3, 25(OH)VD and TBIL level is promoting AS plaque formation in elderly T2DM patients.