Aim To investigate the change of serum small and dense low density lipoprotein cholesterol (sdLDLC) level in patients with coronary heart disease (CHD) after lipid-lowering therapy. Methods Blood samples were collected from 1065 patients with CHD and 469 healthy controls from March to July 2016. Serum low density lipoprotein cholesterol (LDLC), high density lipoprotein cholesterol (HDLC) and sdLDLC levels were measured by direct assay, and serum triglyceride (TG) and total cholesterol (TC) levels were measured by enzyme method. The reference interval of the healthy control group was established. According to the serum LDLC level of CHD patients after lipid-lowering therapy, lipid-lowering LDLC standard group and intensive lipid-lowering LDLC standard group were determined. The blood lipid indexes were compared in each group, and the changes of sdLDLC level and sdLDLC/LDLC ratio were analyzed and compared. Results (1)After lipid-lowering therapy, CHD group compared with the healthy control group, there were significant differences in TG, HDLC and sdLDLC/LDLC ratio between the two groups (P＜0.05), and there were no significant differences in the levels of TC, LDLC and sdLDLC between the two groups (P＞0.05). (2)Compared with the healthy control group, the sdLDLC/LDLC ratio increased in lipid-lowering LDLC standard group (P＜0.05), and there was no significant difference in sdLDLC level between the two groups (P＞0.05). Among the patients who had reached the standard of lipid-lowering, the sdLDLC level of 2.3% CHD patients and the sdLDLC/LDLC ratio of 7.7% CHD patients were higher than the reference interval established by this study. (3)Compared with the healthy control group, SdLDLC level reduced and sdLDLC/LDLC ratio increased in intensive lipid-lowering LDLC standard group (P＜0.05). Among the patients who had reached the standard of intensive lipid-lowering, the sdLDLC level of 0.8% CHD patients and the sdLDLC/LDLC ratio of 15.3% CHD patients were higher than the reference interval established by this study. ConclusionsIn the lipid-lowering therapy and intensive lipid-lowering therapy for CHD patients, the changes of serum sdLDLC level and sdLDLC/LDLC ratio are of great significance for risk analysis of residual cardiovascular events. Lowering sdLDLC level may be one of the important indicators that ultimately reduce the risk of CHD.