Abstract: According to the hot-rolled microstructure of medium manganese steel,a geometry model and initial conditions of intercritical austenitization were established,and the DICTRA dynamic analysis software was used to calculate the austenitization on the martensitic matrix. It is found that supersaturated carbon and manganese in martensite quickly transfer from ferrite to austenite and aggregate at the austenitic side of the phase interface in the initial austenite nucleation stage. In the subsequent transformation,carbon rapidly homogenizes in austenite,but the aggregation degree of manganese in the austenitic side of the phase interface increases. The migration velocity of the austenite phase interface in the initial stage is several orders of magnitude higher than that in the middle and late stages,but rapidly decreases. The phase interface movement in the early transformation stage is dominated by carbon diffusion,but is restricted by manganese diffusion rate in austenite in the middle and late stages. Increasing the temperature can significantly improve the phase interface velocity. Under the condition of achieving the same amount of austenite,the low-temperature and longtime annealing is benefit for manganese transferring from ferrite to austenite and enriching in austenite,which will improve the stability of austenite.