The microstructure and mechanical properties of rolling AZ31 magnesium alloy sheets after annealing at various temperature for different time were investigated by optical microscope (OM), scan electric microscope (SEM) and tensile testing machine. The results suggested that a great amounts of deformation twinning appear after rolling and disappear after annealing at 250~400℃, the recrystallization occurs. The microstructure of the sample annealed at 300℃ for 1 hour is fine equiaxed grain, corresponding to the best effect on mechanical properties. The fracture of the sample after rolling is the quasi-cleavage fracture and is ductile fracture in the annealing sample. The optimal properties are obtained after treatment with rolling at 350℃ and annealing at 300℃ for 1 h. ©, 2014, Northeastern University. All right reserved.