Abstract: The pretreatment and intercritical annealing heat treatment process were designed for medium manganese steel（0.2 C-5 Mn-2.5 Al-0.5 Si,wt%）. The effects of different original microstructure on the microstructure evolution and mechanical properties after intercritical annealing were systematically studied using scanning electron microscopy（SEM）, X-ray diffraction（XRD）, and universal testing machines. The results show that after intercritical annealing treatment, the pretreated P1100-1 sample has a dual phase structure of ultra-fine grained ferrite and retained austenite, and the retained austenite has two different morphologies, namely, lath and granular. During stretching, the pretreated P1100-1 specimen exhibit continuous yield behavior, eliminate the yield plateau phenomenon of the cold-rolled specimen, and has a high-strength yield ratio of 1.61. At the same time, the excellent mechanical properties of the hot rolled sample are obtained: the tensile strength is 1101 MPa, the elongation is 41.21%, and the strong plastic product is 45.37 GPa%.