The invention discloses a preparation method of polyethylene wax micropowder. The preparation method comprises the following steps of: (1) melting and conveying raw materials, i.e., polyethylene wax feed liquid is prepared by adopting a heating device, the polyethylene wax feed liquid is conveyed to an atomizer inside a spray granulation tower by using a heat-insulation gear pump through a pipeline, and the pipeline and other parts of the atomizer, except a spray hole, need to be subjected to integral heat insulation; (2) compressing and atomizing air, i.e., compressed air provided by an air compressor is conveyed into the atomizer through another pipeline and is matched with the polyethylene wax feed liquid with the pressure, the polyethylene wax feed liquid is sufficiently atomized, and the atomized fogdrops are cooled and solidified into micropowder in the granulation tower; and (3) collecting a product, i.e., the cooled and solidified micropowder is collected by using a collecting device to obtain the product. The invention further discloses a spray granulation system which is used for preparing the polyethylene wax micropowder. The preparation method disclosed by the invention is low in energy consumption, simple and convenient to operate and safe and reliable; and the prepared product has small granularity.