Electropulsing treatment (EPT) is a new method to refine the microstructure and improve the mechanical properties of metal materials. In the present paper, the microstructure evolution of rolled AZ31 alloy sheets with 10%, 15% and 20% rolling reduction were investigated by VHX-2000 optical microscope and scanning electron microscope equipped with electron backscattered diffraction (EBSD). After EPT with a pluse-width of 30 μs, a current density of 4.16×109 A/m2, a duty ratio of 0.003 and a processing time of 10min, the average grain size of AZ31 alloy is refined from 150 μm to 20 μm, the tensile strength is improved to 265 MPa and the elongation can reach 19.7%. The affect of the thermal and athermal effect on the recrystallization during EPT was analysied. The result shows that the athermal effect plays a major role in recrystallization and the mechanism of the athermal effect is also revealed.