Abstract: Quenching and partitioning treatment was carried out on the hot-rolled medium manganese steel, and the effects of quenching cooling temperature (195,220,255,280 ℃) on its microstructure, phase composition, hardness, and tensile properties were studied. The results show that lath martensite, massive martensite and residual austenite were found in the medium manganese steel after quenching and partitioning treatment. With increasing quenching cooling temperature, the content of lath martensite decreased, the content of massive martensite increased, and the volume fraction of residual austenite first increased and then decreased, reaching the maximum of 19.81% at quenching cooling temperature of 220 ℃. With increasing quenching cooling temperature, the hardness of the medium manganese steel increased, and the tensile strength, yield strength, and elongation after fracture first increased and then decreased. When the quenching cooling temperature was 220 ℃, the elongation after fracture and the product of strength and elongation of the medium manganese steel were the highest, which were 15.6% and 23.76 GPa·%,respectively.