The invention relates to a technology for diagnosing a bladder cancer through a molecular biology detection means and particularly provides a method for detecting FGFR3 gene mutation to diagnose the bladder cancer and a kit. The technology comprises the step that exons 7, 10 and 15 of an FGFR3 gene are detected to determine whether mutations exist in the exons or not. A double-blind screen test shows that the positive bladder cancer detection rate of the kit is 91.18%, the false positive rate is 3.23%, and the technology has a good clinical application value.