Abstract: The hot deformation behavior of Fe-0.2C-7Mn medium Mn steel at different deformation temperatures (950-1 150℃) and strain rates (0.001-1 s^-1) was investigated by single-pass isothermal compression tests on Gleeble-3500 thermal-mechanical simulator. The processing map of the steel was established by calculating the strain rate sensitivity index, power dissipation efficiency and instability parameters, and the best process window was obtained. The results show that the flow stress of the steel increased with increasing strain rate or decreasing deformation temperature. High deformation temperatures and low strain rates were conducive to the occurrence of dynamic recrystallization. The difference of dynamic recrystallization degree had great influence on strain rate sensitivity index. The instability regions at different true strains appeared in the region of high deformation temperatures and high strain rates, and basically coincided with the low power dissipation efficiency region in the power dissipation map. The best process window for the test steel was deformation temperature of 975-1 100℃ and strain rate of 0.006-1 s^-1.