The standard GB/T 25451-2010 "Beta-ray backscattering method for coating thickness measurement of fuel elements in heavy water nuclear power plants" specifies the method for measuring the coating thickness of fuel elements in heavy water nuclear power plants by beta-ray backscattering method. The standard applies to the measurement of graphite coating on the inner wall of the cladding tube and the coating thickness on the bottom surface of the support pad and the side of the spacer block. The measurement range is 0 to 30 microns. The standard covers measurement methods, equipment requirements, standard samples, environmental conditions and measurement procedures. The method uses the β-ray emitted by the radiation source to backscatter in the coating, and calculates the coating thickness according to the scattering count rate, which provides a standard basis for the accurate measurement of coating thickness.