The normal reference range of C-peptide release test is fasting C-peptide 0.25～0.6nmol/L, and the reference value will be different in each hospital. C-peptide release test is applicable to diabetes mellitus, pancreatic islet cell tumor and pancreatic islet β-cell function lesion, which is helpful for clinical typing of diabetes mellitus (determining whether it is type 1 or type 2 diabetes mellitus) and understanding of pancreatic islet β-cell function; and it is helpful for clinical diagnosis of pancreatic islet cell tumor and evaluation of postoperative effect. The normal reference range of C-peptide release test is fasting C-peptide 0.25～0.6nmol/L, the peak value appears 30～60 minutes after taking sugar (5～6 times of fasting value), and basically returns to the fasting level after 3 hours. Due to the differences between manufacturers and hospital laboratories, the reference values are different, and the specific ones should be referred to local hospitals. Since there is no standardized normal value for C-peptide release test, the specific results and clinical significance of the test should be consulted with a doctor for specific interpretation.