Abstract: The Al-Si-Mn-Cr hot-rolled martensite steel composition system with high M_s phase change point was designed, and 1200MPa hot-rolled martensite steel under this composition system was developed. The mechanical properties were tested, and the microstructure was observed. The effects of Mn content and different coiling temperatures on the microstructure and mechanical properties of hot rolled martensite steel were investigated. The results show that the Al-Si-Mn-Cr hot-rolled martensitic steel can obtain a full martensite structure at a coiling temperature of about 400 ℃, and with the coiling temperature increasing, the martensite structure in the test steel becomes coarser and tends to bainite transform ation, which makes the tensile strength and yield strength of the test steel slightly decrease, and the elongation increases; the increase of Mn content promotes the expansion of the quenched martensite phase region, and the strength of the test steel is greatly improved through the effect of solid solution strengthening. The best strong plastic fit is obtained at the coiling temperature of 410℃ for 1.54% Mn test steel with tensile strength of 1210 MPa, yield strength of 908 MPa, elongation of10.0%, which meets the requirements of GB/T 20887.5-2010.