Abstract: Objective To investigate the correlation between glycated hemoglobin A1c (HbA1c) and the severity of coronary artery disease. Methods 266 patients with coronary heart disease (CHD) diagnosed by coronary angiography were selected. 43 patients with normal coronary arteriography or normal computed tomography coronary angiography (CTA) examination were collected as control group in the same period of the hospital．Gensini score was used to assess the severity of coronary artery lesions and divided into mild, moderate and severe coronary lesions group. Serum HbA1c were compared in each group and the relationship between serum HbA1c and Gensini score were analyzed． Results Compared with the control group, the serum HbA1c levels in t he three coronary heart disease groups were significantly increased (P<0.05)．The levels of serum HbA1c were significantly increased in moderate and severe coronary heart disease groups than those in mild coronary heart disease group (P<0.05). Compared with moderate coronary heart disease group, the levels of serum HbA1c were higher in severe coronary heart disease group (P<0.05). Serum HbA1c levels were positively correlated with Gensini score (r=0.400, P<0.01). Conclusion The level of serum HbA1c is closely related to the degree of coronary artery disease in patients with CHD. The more serious the coronary lesion is, the higher the serum HbA1c level is