Objective To investigate the correlation of fasting plasma glucose(FPG) and glycated hemoglobin A1c(HbA1c)with the severity of coronary artery lesion in the patients diagnosed with acute coronary syndrome (ACS). Methods A retrospective analysis was made of 166 ACS patients admitted to the Department of Geriatrics of the Chinese PLA General Hospital of Eastern Theater Command. According to the degree of coronary artery lesion on Gensini assessment, the patients were divided into mild, moderate and severe stenosis groups. An analysis was made of the correlation of FPG and HbA1c with the degree of coronary artery lesion. SPSS statistics 19.0 was employed for data analysis. Spearman and partial correlation were used for correlation analysis. Logistic regression was performed to analyze the risk factors of severe coronary artery stenosis. Results FPG and HbA1c differed significantly between patients with mild, moderate and severe coronary stenosis (P<0.05). Spearman correlation analysis (r=0.331, P<0.001) and partial correlation analysis (r=0.379, P<0.001) showed that FPG was positively correlated with Gensini score, there was no significant correlation between HbA1c and Gensini score in Spearman correlation analysis (P=0.096), but HbA1c had correlation with Gensini score (r=0.191, P=0.049) performed by partial correlation analysis after controlling related factors. Logistic regression analysis showed that both FPG and HbA1c were independent risk factors for severe coronary stenosis in ACS patients (P<0.05). The area under receiver operating characteristic curve of FPG and HbA1c for predicting severe coronary stenosis were 0.637 and 0.581, respectively, with a sensitivity of 46.0% and a specificity of 86.6% for FPG=7.0 mmol/L, and with a sensitivity of 56.4% and a specificity of 62.5% for HbA1c=6.0%. There was no significant difference in the predictive value of the two indexes (P=0.534). Conclusion FPG and HbA1c are independent risk factors for the degree of coronary artery lesion without significant difference in predicting the occurrence of severe coronary artery lesion.