Two kinds of ultra-high strength cold rolled dual phase steels have been developed by designing C-Si-Mn-Cr and C-Si-Mn-Cr-Mo alloy systems. Tensile strength and elongation of both steels exceed 1100 MPa and 10%, respectively. The microstructures of both steels consist of massive martensite and ferrite. And the massive martensite of Mo-free steel disperses in the ferrite with volume fraction of 64%. However, the massive martensite of Mo-containing steel is connected or closed by small martensite islands each other, and martensite volume fraction is 69%. As to Mo-free steel, the yield strength, yield ratio, and work hardening exponent n are 548 MPa, 0.49, and 0.26, respectively. As for Mo-containing one, the yield strength, yield ratio, and n value are 746 MPa, 0.66, and 0.33, respectively. Besides, the ferrite of Mo-free steel is deformed at the initial stage of plastic deformation. However, for Mo-containing one, Mo solution strengthened ferrite and small overaged martensite islands are deformed prefer-entially at small strain, which causes the yield strength to reach approximately 200 MPa higher than that of Mo-free steel.