Aim To investigate the correlation between small dense low density lipoprotein (sdLDL), high sensitivity C-reactive protein (hs-CRP), mean platelet volume/platelet count (MPV/PLT) and the severity of coronary artery lesions in patients with coronary heart disease. Methods From August 2020 to August 1,0 patients with coronary heart disease who were hospitalized in the Department of Cardiology of Shenzhen Third People's Hospital and underwent coronary angiography were selected. According to the results of coronary angiography, they were divided into single-vessel lesion group (n＝50), double-vessel lesion group (n＝50), and multi-vessel lesion group (n＝50). According to clinical classification, they were divided into stable angina pectoris group (SAP group, n＝26), unstable angina pectoris group (UAP group, n＝48), and acute myocardial infarction group (AMI group, n＝76). Serum levels of sdLDL, hs-CRP, and MPV/PLT were measured among various subgroups, and their correlation with the number and clinical classification of coronary artery disease was analyzed. The ROC curve was used to analyze their effectiveness in predicting the severity of coronary artery disease. Results ①The levels of serum sdLDL, hs-CRP and MPV/PLT in the multi-vessel lesion group were 1.2,1.96 and 1.16 times of those in the double-vessel lesion group (all P＜0.05), and 2.8,3.32 and 1.50 times of those in the single-vessel lesion group (all P＜0.05). Serum sdLDL, hs-CRP and MPV/PLT levels in the double-vessel lesion group were 1.7,1.69 and 1.29 times higher than those in the single-vessel lesion group (all P＜0.05). Serum sdLDL and MPV/PLT levels in AMI group were 1.39 and 1.29 times higher than those in UAP group (all P＜0.05), and 1.37 and 1.38 times higher than those in SAP group (all P＜0.05). There were no significant differences in serum sdLDL and MPV/PLT levels between UAP group and SAP group (P＞0.05). The serum hs-CRP level in AMI group and UAP group was 2.59 and 1.85 times of that in SAP group (both P＜0.05), but there was no statistical significance in hs-CRP level between AMI group and UAP group (P＞0.05). ②Ordered Logistic regression analysis showed that increased levels of serum sdLDL, hs-CRP and MPV/PLT were independent risk factors for predicting the severity of coronary heart disease. ③Spearman correlation analysis showed that serum sdLDL, hs-CRP and MPV/PLT levels were not only positively correlated with the number of coronary lesions (correlation coefficients were 0.5,0.569 and 0.495, respectively, P＜0.05), but also positively correlated with clinical classification of coronary heart disease (correlation coefficients were 0.2,0.40 and 0.414, P＜0.05). ④The ROC curve showed that the combined detection of serum sdLDL, hs-CRP and MPV/PLT was more effective in predicting the severity of coronary heart disease than that of a single indicator detection. Conclusion Increased levels of serum sdLDL, hs-CRP and MPV/PLT are independent risk factors for predicting the severity of coronary heart disease, and are positively correlated with the number of coronary artery lesions and clinical classification of coronary heart disease.