Objective To systematically evaluate the impact of diabetes on the prognosis of bladder cancer patients after radical cystectomy (RC). Methods PubMed, Embase, Cochrane Library database were selected from the inception to the 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 ~ 1.43, P < 0.001) and the risk of tumor-specific death (HR = 1.59, 95%CI: 1.29 ~ 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 underwent RC.