Abstract: In order to improve the mechanical properties of medium manganese steel, a new process of interrupted quenching-carbon partitioning-intercritical annealing was proposed. The medium manganese steel was firstly austenitized at 850 ℃, then quenched to 230 ℃, then heated to 340 ℃ for composition, and finally annealed in the critical zone at 605, 630,655, 680 and 730 ℃ for 1 h. The microstructure and mechanical properties of the medium manganese steel under this process were characterized by tensile testing machine, scanning electron microscope and X-ray diffractometer. The results show that the multi-phase structure composed of lath martensite, fine carbides, retained austenite（RA） and fresh martensite is obtained through this process, and the refined structure matches the austenite with high content and good stability, which is very beneficial to the improvement of mechanical properties of medium manganese steel. Compared with the direct critical area annealing, the plasticity and strong plastic product by using the new process have been improved.