The variation of mechanical properties and fracture morphology of AZ31 Magnesium alloy after laser shock processing (LSP) at different annealing states is investigated．The results show that the hardness of AZ31 Magnesium alloy decreases when the annealing temperature and holding time increase. When the holding time is 30 min, the tensile strength and elongation go up with the annealing temperature rises from 200 ℃ to 350 ℃ while decline quickly when the annealing temperature reaches to 400 ℃ ; when the annealing temperature is 350 ℃ , with holding time goes on, tensile strength reduces gradually but the elongation first increases and then decreases. The best annealing state is 350 ℃ and 30 min when the tensile strength and the elongation at break are 342 MPa and 18% , respectively. Different annealing treatments have apparent effect on the fracture morphology of AZ31 Magnesium alloy after LSP, it presents remarkable toughness fracture surface morphology when the annealing state is 350 ℃ and 30 min.