C-Peptide (C-Peptide) is a connecting peptide composed of 31 amino acids with a molecular weight of about 3021 Daltons. The pancreatic β-cells of the pancreas synthesize proinsulin, which is a very long protein chain. Proinsulin is broken down into three segments under the action of enzymes, and the front and back segments are reconnected to become insulin, which is composed of an A and a B chain, while the middle segment is independent and is known as the C-peptide. Insulin and C-peptide are secreted in equimolar concentrations, and after entering the blood, most of insulin is inactivated by the liver, while C-peptide is rarely taken up by the liver, plus C-peptide degradation is slower than insulin, so the concentration of C-peptide in the blood is higher than that of insulin, usually more than 5 times, so C-peptide more accurately reflects the function of pancreatic islet β-cells. The measurement of the level of C-peptide can be used for the classification of diabetes mellitus and to understand the function of pancreatic β-cells of diabetes mellitus patients. C-peptide level measurement can be used to classify diabetes and understand the function of pancreatic β-cells in patients with diabetes. Currently, C-peptide measurement methods widely used in medical clinics include radioimmunoassay, enzyme immunoassay, electrochemiluminescence, chemiluminescence.