In order to improve the plastic deformation capacity of magnesium alloy, tensile tests of AZ31 magnesium alloy accompanied with high intensity pulse current were carried out. The effects of pulse current on microstructure and tensile deformation behavior of the alloy were investigated and the mechanisms were examined as well. The results show that the deformation resistance of AZ31 magnesium alloy with pulse current greatly decreases compared with that without pulse current, and the extent of decline raises as current density increases. The dynamic recrystallization (DRX) occurs in the alloy with pulse current during the tensile testing, and obtain fine recrystallized structure, which can bring down the deformation resistance. The rapid recrystallization behavior is based on the enhancement of atomic diffusion and acceleration of the grain boundary transformation from small angle to large angle resulting from pulse current. On the other hand, the increasing of the plastic deforming ability of the alloy was attributed to the electric effect of the pulse current, which can change the activation energy of dislocations and promote the mobility of dislocations.