Background <p>Metabolic syndrome (MS) is a risk factor for renal calculi development. This investigation intended to explore the associations of MS and its components with complex renal calculi and stone composition.</p> Methods <p>The study involved 465 patients with renal calculi who underwent surgical treatment at Sichuan Provincial People's Hospital. Patients were classified into non-complex and complex renal calculi groups. In the complex renal calculi group, patients were divided into subgroups based on the presence of MS, and separately based on abnormal MS components. Differences in stone size and composition among these subgroups were evaluated. Multivariate logistic regression analysis was used to identify key MS components associated with the progression of complex renal calculi, based on comparisons between non-complex and complex renal calculi patients.</p> Results <p>A total of 465 patients with renal calculi were included, of whom 197 had complex renal calculi. In patients with complex renal calculi, MS, high fasting blood glucose (FBG), and dyslipidemia were associated with larger stone size. Patients with MS had higher ammonium magnesium phosphate hexahydrate (MAP) and uric acid (UA) stone proportions. Patients with high body mass index (BMI) had a higher UA stone proportion. The carbonate apatite and MAP stone proportions were higher, while the calcium oxalate monohydrate stone proportion was lower in patients with high FBG. Multivariate logistic regression analysis revealed that BMI (OR = 1.214, 95% CI: 1.033–1.295), FBG (OR = 1.795, 95% CI: 1.359–2.285), and high-density lipoprotein cholesterol × 10 (HDL-C × 10; OR = 0.301, 95% CI: 0.210–0.421) were independently associated with complex renal calculi.</p> Conclusion <p>Elevated BMI and FBG, along with reduced HDL-C, are associated with the presence of complex renal calculi. Monitoring these factors may improve disease management.</p>