Abstract: The diagnosis methods in the world for the fuel failures in PWR and the existing problems of diagnosis methods are analyzed and improved from three aspects, which are the number of failed fuel rods, fuel failure size and burnup of failed fuel. The factors that may affect the diagnosis result are also identified and discussed. The operating data of Chinese in-service nuclear power plants are used to verify the improved diagnosis method, and the results show that, the improved diagnosis method for fuel failures can accurately diagnose the fuel failure and has a wider applicability.