A low-pressure casting bottom mold for an aluminum alloy hub is provided. The low-pressure casting bottom mold for the aluminum alloy hub is composed of an upper surface facing a cavity and a lower surface facing a die casting platform, wherein the bottom mold lower surface facing the die casting platform comprises an iron sheet cover, the iron sheet cover is fixed at a position, corresponding to a wheel spoke, of the bottom mold lower surface, and a sealed space is formed between the iron sheet cover and the bottom mold lower surface in a surrounding manner; the iron sheet cover comprises air inlets at one side close to a wheel center and air outlets at one side close to a rim; and the air inlets are connected with air tubes.