Abstract: The microstructure,mechanical properties and impact fracture morphologies of 17-4PH stainless steel were analyzed by using four different heat treatment processes(solution and aging).The effect of different treatment processes on mechanical properties of 17-4PH stainless steel was investigated.The results indicate that the tensile strength of the samples without intermediate treatment declined while the plasticity and toughness increased with the aging temperature rising.And the impact fractures were all typical cleavage brittleness.The plasticity and impact property of the samples with intermediate treatment were obviously better than that of the others without intermediate treatment,though the tensile strength was less.And the impact fracture was obviously ductile fracture.The microstructure of the martensite with intermediate treatment was homogeneous and fine.