Magnesium alloys have poor plasticity at room temperature, which leads to uneven distribution and stress difference of microstructure during rolling. Therefore, it is important to analyze the mechanical characteristics and microstructure evolution from the angle of material properties. Based on this, a piecewise constitutive model of AZ31 magnesium alloy was established by experiments, and a cellular automata model including grain topology technology was constructed. With the aid of secondary development technology, the constitutive model, cellular automata and finite element software were combined to simulate, and the predicted results including stress, strain, grain size and distribution law were obtained. It is of certain significance to control the forming process of AZ31 magnesium alloy rolled by Pilger to realize the coordinated control of forming and properties, and the simulation results were verified by experiments.