Abstract: A large size of super-high-strength maraging stainless steel Cr-Ni-Co-Mo bar has been developed.Effects of heat treatment on mechanical properties of Cr-Ni-Co-Mo maraging stainless steel with eight different components were shudied.Through further optimization of the alloy composition:a high-strength(Rm=1 940 MPa),high-ductile (AKU2=55 J and KIC=104 MPa·m) maraging steel has been obtained.Good technological properties of this kind of steel make it suitable to be used as critical components with high strength and toughness and sea water corrosion-resistantce.It also reveals broad application prospects in aerospace,aviation and other fields.