Abstract: The nuclear power turbine wheel disk was treated by shot peening. The domain size, micro-strain, residual stress and micro-hardness of the shot peened surface layer were analyzed by X-ray diffraction stress analyzer and hardness tester. The results show that the microstructure of the shot peened surface layer refined and the micro-strain occured on it. The domain size and micro-strain of the wheel disk after shot peening were 24 nm and 2.9×10-3, respectively. The microstructure strengthen effect was obviously, meanwhile, the refined microstructure had a gradient distribution. The distribution of micro-hardness was according with the distribution of refined microstructure with the depth. The maximum values of 601 MPa in residual pressure stress and 398 HV in the micro-hardness were given on the spot peened surface, then the values gradually decreased from the surface to the centre.