Abstract: C-Si-Mn-Cr-Nb and C-Si-Mn-Nb Ultra-high strength dual phase steels were piloted in laboratory. The effect of Cr on transformation of high strength cold rolled dual phase steels was analyzed by using the thermal dilatometer. Optical microscopy, scanning electron microscopy and the tensile tests were used to characterize the microstructures and to determine the mechanical properties. The results show that, the CCT curve of tested steel which had Cr was shift to right. Cr markedly retards ferrite and pearlite transformation, and markedly reduces the finish temperature of ferrite transformation and the transformation temperature of bainite and martensite, but had less effect on the start temperature of the ferrite transformation and increased the harden-ability of the austenite. The tested steel has the F+M more easily including Cr in the same cooling rate. Cr have the well influence on the microstructure of the dual phase steel, make the grain refinement , the yield strength was increased from 510MPa to 535MPa and the tensile strength was raised from 1080MPa to 1150 MPa, With the tensile strength increasing the elongation was raised.