Objective To explore the diagnostic value of serum C-peptide combined with glyclated hemoglobin A1c test in the clinical diagnosis of type 2 diabetes mellitus.Methods A total of 130 patients with suspected type 2 diabe-tes mellitus admitted to Qixia City People's Hospital from July 2022 to June 2023 were selected as the research ob-jects.All patients received serum C-peptide and glyclated hemoglobin A1c tests.Taking oral glucose tolerance test as the gold standard,the diagnostic results and diagnostic efficacy of single and combined tests of serum C-peptide and glycated hemoglobin A1c were compared.Results The results of oral glucose tolerance test showed that 108 patients were diagnosed as positive and 22 patients were diognosed as negative.The combined test of serum C-peptide and gly-cated hemoglobin A1c showed that 107 cases were positive and 23 cases were negative,with a detection rate of 82.31%(107/130).The accuracy,sensitivity,specificity,positive predictive value and negative predictive value of se-rum C-peptide combined with glycated hemoglobin A1c test were higher than those of serum C-peptide and glycated hemoglobin A1c single test,and the differences were statistically significant(all P<0.05).Conclusion In the diagnosis of type 2 diabetes mellitus,compared with the single index test,the detection rate and accuracy of serum C peptide combined with glycated hemoglobin A1c test are higher,which can make accurate judgment on the patient's condi-tion,so as to ensure the feasibility of treatment.