Objective: To explore the changes and clinical significance of serum glucagon-like peptide 1 (GLP-1) level in patients with type 2 diabetes mellitus complicated with metabolic syndrome. Methods: A total of 24 patients with type 2 diabetes and 40 patients with type 2 diabetes combined with metabolic syndrome admitted to our hospital from January 2018 to December 2020 were included in this study. Twenty-one healthy subjects who came to the hospital for physical examination during the same period were selected as the control group. Patients’ gender, age, waist circumference, abdominal obesity, duration of diabetes, systolic and diastolic blood pressure, glycosylated hemoglobin (GHb), fasting blood glucose, triglyceride (TG), low density lipoprotein (LDL-C), high density lipoprotein (HDL-C), total cholesterol and TNF alpha were collected. The differences of the above indexes and the correlation between GLP-1, TNF-α and other indexes in the three groups were analyzed. Results: There was no significant difference in age and sex among the three groups (P>0.05). Compared with the control group, the levels of waist circumference, BMI, systolic blood pressure, diastolic blood pressure, fasting blood glucose glycosylated hemoglobin, TC, TG, HDL-C, TNF-α and GLP-1 in diabetic patients with metabolic syndrome group were different (P<0.05). Compared with diabetic group, waist circumference, BMI, systolic blood pressure, diastolic blood pressure, glycosylated hemoglobin, TG, HDL-C, TNF-α and GLP-1 levels in diabetic patients with metabolic syndrome were significantly different (P<0.05). The expression of GLP-1 was negative correlated with TC, waist circumference, TNF-α, TG, systolic blood pressure, diastolic blood pressure, HbA1c and fasting blood glucose. Conclusion: GLP-1 levels are associated with the progression of type 2 diabetes mellitus, and are negatively correlated with TNF-α, TC, waist circumference, TG, systolic blood pressure, diastolic blood pressure, HbA1c, and fasting blood glucose.