Abstract: The medium manganese steels for automobile were treated by preheating at different temperatures (150, 550, 600, 750 ℃), quenching at 750 ℃, cryogenic treatment at -75 ℃, respectively, and then were subjected to reverted transformation annealing. The microstructure and mechanical properties after different heat treatments were studied. The results show that the retained austenite content in medium manganese steel after preheating was higher than that in as-cast steel. The volume fraction of the retained austenite reached the maximum value of 42.2% after preheating at 600 ℃, and the microstructure was composed of block/strip martensite and retained austenite. With the increase of preheating temperature, the tensile strength of medium manganese steel after reverted transformation annealing increased, and the elongation after fracture and the product of strength and elongation increased first and then decrease. When the preheating temperature was 600 ℃, the product of strength and elongation reached the maximum value of 51.99 GPa·%. Compared with those after quenching and reverted transformation annealing, the tensile strength and yield strength of the medium manganese steel after cryogenic treatment and reverted transformation annealing were smaller, and the elongation after fracture, the product of strength and elongation and the impact energy at -40 ℃ were higher.