The semi-solid slurry of AZ31 magnesium alloy was manufactured by gas bubbles stirring. The effects of stirring temperature and stirring time on the microstructure of semi-solid slurry were researched. The results indicate that it is feasible to manufacture the slurry with particle-like primary phases. When the stirring temperature is higher, the morphology of the primary a-Mg presents rosette-like morphology and the size of grain is coarse, and the morphology mainly was α- Mg dendrite at lower stirring temperature. Long stirring time could reduce dendrites and liquid phase, and made the non-dendritic grains well spheroidized. But the effects of longer stirring on shape and size of primary particles are not significant. The optimal process parameters for ideal semi-solid slurry manufactured were stired 3min at 645°C.