The microstructure is characterized in that dispersed ε-carbides are precipitated in lath martensite and bainite ferrite after low temperature tempering, resulting in second phase dispersion strengthening. At the same time, the undecomposed retained austenite has high stability due to thermal stabilization and mechanical stabilization, which gives full play to solid solution strengthening, dispersion strengthening, substructure strengthening and phase transformation strengthening in the structure, thus obtaining ultra-high strength for steel. However, the release of residual stress, the formation of tempered martensite and the presence of a certain amount of stable retained austenite during tempering have significantly improved the plastic toughness of the steel