The invention discloses a preparation method of a polyethylene film, and the method comprises the following steps: step (1) taking a mixed liquid I as a carrier flow to convey a main catalyst in a catalyst system to a reactor, wherein the mixed liquid I comprises alkane, alkene and a co-catalyst, adding supplementing alkene feedstock into a material flow II which outflows from the reactor to obtain a material flow III and dividing the material flow III into a material flow IIIa and a material flow IIIb, wherein the material flow IIIa and the material flow IIIb separately flow back to the lateral part and the bottom of the reactor, and performing polymerization in the reactor to obtain an ethylene polymer and performing discharging from the reactor, wherein, the alkene comprises alpha-alkene and ethylene, and the molar ratio of the alpha-alkene and the ethylene is more than or equal to 1; and step (2) performing a blow molding process on the ethylene polymer prepared through the step (1) to obtain the polyethylene film. The method provided by the invention increases the self-adhesive property and decreases the haze of the obtained polyethylene film.