Abstract: The equal channel angular pressing （ECAP） was used to make large plastic deformation of magnesium alloy， and ECAP processing and relevant process parameters were obtained by using finite element method. The strain distributions in the workpieces and the loads on the dies were studied. The mathematical model of accumulated deformation results， microstructure refinement and mechanical properties were established. Through the analysis， the relationships between grain refinement and mechanical properties were obtained. The refined grain size and the obtained mechanical properties are forecasted by using characterization of accumulation deformation.