In order to improve the strength-ductility balance of medium manganese steel for automobiles, cold-rolled medium manganese steel was treated by annealing at different temperatures (650-680 ℃) and for different time (10-50 min) for austenitic reverse transformation. Then, effects of annealing temperature and holding time on the microstructure and mechanical properties of medium manganese steel were explored. It is found that the microstructure of the original cold-rolled medium manganese steel plate is composed of ferrite (F) and martensite (M), and the dispersed carbides with sizes ranging from 20 nm to 45 nm can be observed in the microstructure. As the annealing temperature rises from 650 ℃ to 680 ℃, the yield strength, elongation, strength-ductility balance, and residual austenite volume fraction of medium manganese steel increase followed by a decrease, but tensile strength increases all the time. As the annealing time is prolonged from 10 min to 50 min, the yield strength, tensile strength, elongation, strength-ductility balance and residual austenite volume fraction of medium manganese steel decrease after an initial increase. It is found that after annealing treatment at 660 ℃ for 30 min, the cold-rolled medium manganese steel has a structure composed of F + M + austenite (γ), with austenite at a volume fraction of 24.12%, ultrafine grained ferrite with an average grain size of 0.29 μm, lath martensite with an average wideness of 0.27 μm, and strength-ductility balance of 23.33 GPa·%.