<p>In this study, the third-generation advanced high-strength 10Mn5 medium-manganese steel (medium-Mn steel) sheet was successfully used to stamp the structural parts of the automobile A-pillar beam reinforcement plate. The finite element (FEM) simulation of its stamping process was carried out, and the simulation and experimental results were compared in terms of forming state, thinning rate distribution and the equivalent plastic strain (EPS) distribution. A numerical simulation platform suitable for the forming process of medium-Mn steel was established. Different EPS regions in the stamped automobile structural part were selected as the research objects, the dynamic deformation law and the characteristics of phase transformation induced plasticity (TRIP) were investigated by correlating macroscopic strain with microscopic austenite phase evolution. The grid method and magnetic characterization were used to quantify the plastic deformation and austenite transformation in different regions of the formed part, and the relationship between the EPS and the austenite volume fraction was fitted, which was verified based on the OC model martensite transformation formula. A quantitative relationship between the amount of plastic deformation and microstructure evolution during dynamic deformation of medium-Mn steel was established. The 10Mn5 steel nanoindentation hardness was studied to measure the mechanical properties after forming. The relationship between EPS and material hardness was established, enabling the establishment of a three-dimensional evolution relationship among plastic deformation, deformation microstructure, and mechanical properties of medium-Mn steel structural parts during the stamping process.</p>