OBJECTIVE: This study aimed to examine the relationship between the Atherogenic Index of Plasma (AIP) and the severity of coronary artery stenosis in patients with type 2 diabetes mellitus (T2DM). METHODS: In this retrospective cross-sectional study, 303 T2DM patients who had not been treated with statins and underwent coronary computed tomography angiography (CCTA) were included. AIP was calculated as log10(TG/HDL-C). The severity of coronary stenosis was assessed using standard quantitative measures. Participants were divided into four groups based on AIP quartiles (Q1 to Q4). Statistical analyses involved correlation tests, multivariable logistic regression, and receiver operating characteristic (ROC) curve analysis. RESULTS: A clear dose-response trend was found between increasing AIP quartiles and greater severity of coronary stenosis (P for trend <0.01). The median AIP was significantly higher in patients with severe stenosis (≥70%) compared to those with non-obstructive disease (0.14 vs. 0.05, P<0.001). After adjusting for multiple variables, AIP remained independently associated with obstructive stenosis (≥50%), with an odds ratio of 3.93 (95% confidence interval: 1.70-9.62). The area under the ROC curve (AUC) for AIP was 0.598 (95% CI: 0.540-0.653), which was significantly better than that for LDL cholesterol (0.481, P = 0.032) and HDL cholesterol (0.384, P<0.001). CONCLUSION: Higher AIP levels are independently associated with more severe coronary stenosis in patients with T2DM and demonstrate superior discriminative ability compared to traditional lipid markers in this cross-sectional cohort. Therefore, AIP may be considered an adjunctive biomarker for cardiovascular risk stratification in this high-risk population, pending prospective validation.