Abstract: Based on the traditional martensitic aging steels, a new type of high alloy ultra-high strength steel powders (Fe–18.0Co–15.0Ni–8.0Mo–3.0Cr–0.5Cu–0.4Nb–0.4V–0.2Al) was designed by increasing the content of Co and Mo elements. The high alloy ultra-high strength steel powders were prepared by water-gas combined atomization method. The sintered samples were prepared by metal powder injection molding process, and then subjected to solution treatment, deep cryogenic treatment, and aging treatment. The raw material powders and high alloy ultra-high strength steel samples were observed and tested by laser particle size distribution analyzer, scanning electron microscope, and universal mechanical testing machine. The results show that the raw material powders prepared by water-gas combined atomization method have the high sphericity, the content of each element in the powders is close to the designed composition, and the content of impurity elements is low. The relative density of the high alloy ultra-high-strength steel samples prepared by metal powder injection molding reaches 98.7% with the excellent mechanical properties. The yield strength is 1824 MPa, the tensile strength is 2053 MPa, and the elongation is 7.9%. Compared with the traditional 18Ni (200) martensitic aging steels, the prepared samples show more outstanding comprehensive mechanical properties.