The study investigated the relationship between residual cholesterol (RC) and the severity of coronary artery stenosis in 155 patients with type 2 diabetes. The results showed that patients with moderate to severe stenosis had higher levels of residual cholesterol than patients with mild stenosis. Residual cholesterol showed a positive correlation with the Gensini score, which measures the severity of stenosis. Multivariate analysis confirmed that residual cholesterol is an independent risk factor for the severity of coronary artery stenosis (OR = 2.849). When residual cholesterol was added to the basic prediction model, diagnostic accuracy improved significantly (AUC increased from 0.603 to 0.790). The study concluded that residual cholesterol may serve as an auxiliary indicator for risk stratification of coronary artery stenosis in patients with type 2 diabetes and has incremental diagnostic value in addition to traditional risk factors.