In order to study the effect of laser shock processing (LSP) on the properties of magnesium alloy, according to the laser technology parameters after optimization, Rolled AZ31B magnesium alloy sheets surface were processed with Ndglass laser. Test results showed that grain is refined obviously , grain size changes from about 20 μm to 10 μm. Residual compressive stress induced by LSP reached up to -126 MPa. At room temperature, through three points loading method, samples performed by LSP, local regional LSP and without LSP were immersed in deionized water to carry out stress corrosion experiment. Macroscopical and microcosmical analysis was applied to its fracture surface.It shows that LSP completely prevents stress corrosion cracking (SCC) initiation for AZ31B in deionized water, and it indicats that LSP inhibits the propagation of the SCC crack.