Abstract: The research situation and development trend of medium Mn steels were summarized. The effects of alloy elements on the microstructure and properties were introduced in detail. The process design, microstructure evolution law and deformation behavior of medium Mn steels were summarized. The plastic instability phenomenons of medium Mn steels were analyzed and discussed, and the feasible suggestions of eliminating the plastic instability phenomenons were proposed on the premise of guaranteeing the excellent mechanical properties of medium Mn steels.