The invention provides tensile strength 1000 MPa-grade cold-rolled complex phase steel and a preparation method thereof. The complex phase steel is composed of, by mass, 0.07-0.13% of C, 0.2-0.4% of Si, 1.8-2.5% of Mn, 0.2-0.6% of Cr, 0.1-0.4% of Mo, less than or equal to 0.02% of P, less than or equal to 0.015% of S, 0.02-0.06% of Nb, 0.02-0.06% of Ti and the balance iron and other inevitable impurity elements. The complex phase steel adopts low carbon equivalent design as composition design and has good welding performance, a small amount of microalloy elements of Nb and Ti and C elements are composited and added for forming nanometer precipitated phases, thus, grains are refined, meanwhile, the elements are dispersed and distributed in a complex phase steel ferritic matrix, sufficient precipitation strength is reached, therefore, the yield strength of a material is improved, the good bending and reaming properties are achieved, the tensile strength of the final cold-rolled complex phase steel is 1000 MPa or higher, the yield strength reaches 780 MPa or higher, the yield ratio is 0.8 or higher, the elongation after fracture is 8% or higher, the reaming ratio is 50% or higher, andthe application requirements in the field of automotive steel are met.