Aim To investigate the effects of proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors on the incidence of restenosis 1 year and major adverse cardiovascular and cerebrovascular events (MACCE) 3 years after percutaneous coronary intervention (PCI) in elderly patients with diabetes and acute coronary syndrome (ACS). Methods 320 elderly patients with diabetes and ACS were randomly divided into the conventional treatment group and PCSK9 inhibitor group, with 160 cases in each group. The conventional treatment group received standardized drug treatment after PCI, while the PCSK9 inhibitor group received PCSK9 inhibitor in addition to standardized drug treatment for a course of 1 year. The total cholesterol (TC), triglyceride (TG), high density lipoprotein cholesterol (HDLC), low density lipoprotein cholesterol (LDLC), lipoprotein (a), high sensitivity C-reactive protein (hs-CRP), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and other test indicators as well as the incidence of restenosis at PCI site were observed in the two groups of patients, and the primary endpoint (myocardial infarction, cardiac death, and all-cause death), the composite endpoint (myocardial infarction, cardiac death, ischemia-driven repeat revascularization, stent thrombosis, and stroke) of the secondary endpoint (MACCE) and the incidence of angina pectoris and hospital readmission were comparatively analyzed through 3-year follow-up. Results After 1 year of treatment, the levels of TC, TG, LDLC, lipoprotein (a), hs-CRP, TNF-α, IL-6, and the incidence of restenosis in the PCSK9 inhibitor group were significantly lower than those in the conventional treatment group (P＜0.05). The 3-year follow-up results showed that the primary endpoint events (cardiac death, myocardial infarction), total MACCE, stent thrombosis, angina recurrence, and repeat revascularization incidence in the PCSK9 inhibitor group were significantly lower than those in the conventional treatment group (P＜0.05). Conclusion PCSK9 inhibitors can effectively reduce the blood lipid level, inhibit inflammatory reaction, and reduce the incidence of restenosis 1 year after PCI and MACCE 3 years after PCI in elderly patients with diabetes and ACS.