Abstract: 17-4PH stainless steel was aged at 460-580 ℃ for 4 h. The effects of different temperatures aging on the microstructure and mechanical properties of 17-4PH stainless steel were studied by means of microstructure observation, XRD analysis, tensile test, hardness test and impact test. The results show that the microstructure of 17-4PH stainless steel aged at different temperatures is mainly martensite, carbide and a small amount of reverse austenite. With the increase of aging temperature, the martensite in 17-4PH stainless steel is gradually coarsened, the reversed austenite content gradually increases, the hardness, tensile strength and yield strength gradually decrease, the elongation and impact absorption energy gradually increase.When the aging temperature increases from 460 ℃ to 580 ℃, the hardness of 17-4PH steel decreases by 26.2%, and the impact absorption energy increases by 299.5%. The toughness of 17-4PH stainless steel is significantly affected by aging temperature.The tensile fracture of 17-4PH stainless steel is mainly composed of dimples and torn edges.With the increase of the aging temperature, the number of dimples on the tensile fracture increases significantly, and the dimple size is increased, the dimples become deeper, the distribution is more uniform, and the plasticity of the stainless steel increases.