Equal channel angular pressing (ECAP) is one of the important methods for achieving severe plastic deformation in magnesium alloys. In order to further reveal the recrystallization mechanism of ECAP samples under different conditions, through the finite element simulation and experiment on AZ80 magnesium alloy, the deformation characteristics and microstructure evolution of the samples in different deformation regions, under different deformation temperatures and extrusion passes were studied. The results indicate that the proportion of high-angle grain boundaries in the microstructure is significantly higher during severe plastic deformation, indicating that discontinuous dynamic recrystallization is the main recrystallization mechanism in the ECAP process. Magnesium alloys subjected to singlepass ECAP exhibit significant differences in microstructure at similar temperatures (360 ℃ and 380 ℃), showing strong temperature sensitivity. The difference of the average equivalent strain and its variation are significant among different deformation paths for multi-pass ECAP. The interaction between the heating process and multi-pass extrusion jointly promotes the optimization of the microstructure of magnesium alloys and the improvement of grain properties.