Globally, both the incidence rates of diabetes mellitus and bladder cancer have continued to rise, which have seriously endangered human health. It has been found that there may exist some underlying mechanisms in the occurrence and development of these 2 diseases, which then may affect the incidence and prognosis of bladder cancer in diabetes mellitus patients. Some studies suggest that there is a complex relationship between them, but there are different opinions on the results at the same time. This article reviewed the epidemiological characteristics, common risk factors, effects of hypoglycemic drugs on bladder cancer, possible mechanism of diabetes affecting the occurrence of bladder cancer, and impact of diabetes on the prognosis of bladder cancer.