Objective. To systematically evaluate the impact of diabetes on the prognosis of bladder cancer patients after radical cystectomy (RC). Methods. PubMed, Embase, and Cochrane Library databases were selected from inception to October 2021. The studies on the effects of diabetes on bladder cancer patients after RC were included for analysis. The inclusion and exclusion criteria were independently selected for literature screening, the quality of the included studies was evaluated, and data were extracted. Results. A total of 5 cohort studies were included, with a total of 2 661 subjects, including 391 cases in the diabetic group, non-diabetes. Meta-analysis results show that diabetes increases the overall risk of death in patients after RC (HR = 1.36, 95% CI: 1.30 similar to 1.43, P < 0.001) and the risk of tumor-specific death (HR = 1.59, 95% CI: 1.29 similar to 1.95, P < 0.001). Sensitivity analysis shows that the stability of this study is well. Conclusion. Diabetes was an independent risk factor in terms of overall and cancer-specific survival in patients who underwent RC.