The present invention provides an aripiprazole sustained release microsphere and a preparation method thereof, and the microsphere comprises aripiprazole and poly(lactide-co-glycolide), wherein the microsphere shows a spherical network framework structure with reticular pores being distributed over the spherical surface, and aripiprazole is filled in the pores. The microsphere has an average particle size of less than 20 µm, and the content of aripiprazole is 65%-80% of the total weight of the microsphere. Since the aripiprazole sustained release microsphere of the present invention has an average particle size of less than 20 µm, it is applicable to a 5-gauge needle, thereby reducing pain in patients. In addition, the microsphere of the present invention can quickly reach an effective drug concentration in the early stage of administration without the need for oral administration to achieve the therapeutic effect, and does not generate a burst release effect.