To investigate the correlation between residual Syntax score (rSS) and long-term prognosis in diabetic patients with renal insufficiency undergoing percutaneous coronary intervention (PCI).In this retrospective study, we included 510 patients with coronary heart disease, diabetes, and renal insufficiency who received PCI at the Third People's Hospital of Chengdu from July 2018 to December 2020. Patients were divided into three groups based on their eGFR levels: 113 patients with eGFR ≥ 60 mL/min/1.73 m2, 256 patients with eGFR between 30 and 60 mL/min/1.73 m2, and 141 patients with eGFR 8 indicating incomplete revascularization. We collected baseline data on cardiovascular adverse events and followed up with patients for 12 months, analyzing the correlations between rSS and biochemical markers such as blood glucose, uric acid, urea, serum creatinine, and eGFR, as well as the relationship between major adverse cardiovascular events (MACE) and rSS.Univariate analysis identified myocardial infarction (MI), β-blocker use, and follow-up duration as factors significantly associated with the long-term prognosis of diabetic patients with renal insufficiency after PCI (P < 0.05). MI (OR=3.053, P=0.009), β-blocker use (OR=3.134, P=0.009), and follow-up duration (OR=0.998, P=0.05) were independent risk factors for long-term prognosis in these patients. rSS was positively correlated with blood glucose (r=0.973, P=0.000), uric acid (r=0.933, P=0.000), urea (r=0.907, P=0.000), serum creatinine (r=0.588, P=0.000), and eGFR (r=0.623, P=0.000). Syntax score was also positively correlated with long-term prognosis (OR=0.138, P=0.001).The rSS is a valuable tool for evaluating independent risk factors such as incomplete revascularization, MI, β-blocker use, and follow-up duration, all of which are positively correlated with the long-term prognosis of diabetic patients with renal insufficiency after PCI.