Objective To investigate the efficacy of Changxin Decoction in the treatment of angina pectoris and the potential mechanism. Methods Angina pectoris patients with interaction of phlegm and blood stasis were randomly divided into control group and treatment group, with 40 cases in each group. The control group received standard Western medicine treatment, while the treatment group was given Changxin Decoction in addition to standard Western medicine treatment. The two groups were evaluated for the outcomes of angina pectoris and traditional Chinese medicine (TCM) syndrome, as well as the changes in the levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), lipoprotein (a) ［Lp (a)］, high-sensitivity C-reactive protein (hs-CRP), fasting plasma glucose (FPG), glycosylated hemoglobin A1c (HbA1c), and proprotein convertase subtilisin/kexin type 9 (PCSK9), after treatment. Results The treatment group had significantly better outcomes of angina pectoris and TCM syndrome than the control group (P<0.05). After treatment, the control group showed no significant changes in the levels of hs-CRP, TC, LDL-C, HDL-C, Lp (a), FPG, HbA1c, and PCSK9 (P>0.05), while the treatment group showed significant reductions in the levels of hs-CRP, TC, LDL-C, Lp (a), and PCSK-9 (P<0.05); the treatment group had significantly greater reductions in the levels of hs-CRP, TC, LDL-C, and PCSK-9 (P<0.05). Conclusion In the treatment of angina pectoris with interaction of phlegm and blood stasis, Changxin Decoction can decrease blood PCSK9 level to reduce blood lipids and inflammatory response, thus improving atherosclerosis.