Abstract: The influences of powder raw materials, Mo content and different forging and tempering temperatures on the combined mechanical properties and structures of Fe-Ni-Mo-C system powder forging steel have been stndied. Fe-2Ni-0.5Mo-0.25C powder forging steel with a density of 7.7g/cm³ made from water atomized 4600 alloy powder has optimum combined mechanical properties ater carbonizing, hardening and tempering. Its impact toughness is 32J/cm², ultimate tensile strength is 1280MP and hardness is HRC53.7.