Abstract: The microshear test has been developed to investigate the microshear strength of AP1000 Nuclear Steam Turbines rotor and its narrow gap welded joints. According to the relationship between shear strength and yield strength of metal, yield strength of the whole welding joints could be obtained. The influence of welding joint property nonuniformity on the J-integral was investigated by using finite element method. The simulated results indicated that the increase of the load may get rise in the value of J-integral. When the load inceases to 0.8 times the limit load,crack tip enters into plastic area and the value of J-integral increases rapidly. For the same crack length and load,the J-integral value of under-matched area is higher than the one of the over-matched area,but the property nonuniformity of matching in loading area will cause the fluctuation of J-integral value.