Abstract: The Johnson-Cook constitutive equation of AZ31 Mg alloy was established, and the FEM model of the cumulative plastic deformation combined the equal channel angular pressing and forward extrusion (ECAP-FE) was constructed, the simulation of the ultrasonic vibration assisted ECAP-FE of AZ31 Mg alloy was carried out. The effect of ultrasonic vibration applied method on the ECAP-FE process was studied. The results show that applying ultrasonic vibration can improve the uniformity of equivalent strain value and strain distribution, reduce equivalent stress and forming load, while also improving the material's plastic forming ability and deformation amount, promoting the material's dynamic recrystallization process during plastic deformation, which further refines the grains. Compared with those of the convectional ECAP-FE, the effect of applying both transverse and longitudinal ultrasonic vibrations simultaneously is best, the forming load drops by 28%, whereas the maximum plastic strain rises by 36.4%. Followed by single longitudinal ultrasonic vibration, and single transverse ultrasonic vibration has the worst effect.