Abstract: The microstructure and mechanical properties of 0.12C-0.78Si-1.42Mn-0.74Al-0.32Mo steel under four different multi-pass deformation and controlled cooling after rolling were studied by using of a physical simulation system. The results show that different multi-phase structures (ferrite/bainite and bainite/martensite) can be achieved in the steel under multi-pass deformation at high temperature through the physical simulation system and controlling cooling treatment. The yield strength, tensile strength and total elongation of the steel with the ferrite/bainite structure are 388~558 MPa, 681~838 MPa, and 15%~27%, respectively; but the yield strength, tensile strength, and total elongation of the steel with the bainite/martensite structure reach 746 MPa, 960 MPa, and 19%, respectively.