The invention discloses a ball mill which comprises a stator cylinder body consisting of a bottom surface, an outer-circle cylinder wall and an inner-circle cylinder wall and a rotor cylinder body consisting of a top surface, a rotor cylinder wall, a central post and a connecting shaft, wherein the rotor cylinder wall is arranged between the outer-circle cylinder wall and the inner-circle cylinder wall, the central post is arranged in the inner-circle cylinder wall, an outer-circle grinding cavity is formed between the outer-circle cylinder wall and the rotor cylinder wall, a middle-circle grinding cavity is formed between the rotor cylinder wall and the inner-circle cylinder wall, and an inner-circle grinding cavity is formed between the inner-circle cylinder wall and the central post, so that the ball mill disclosed by the invention is provided with three grinding cavities, and the material enters from a material inlet, and is sequentially ground by the outer-circle grinding cavity, the middle-circle grinding cavity and the inner-circle grinding cavity, screened by a screening device, and discharged outside a material outlet, therefore, compared with the ball mill which is provided with only one grinding cavity, the ball mill is higher in grinding quantity, and higher in grinding efficiency.