The invention discloses a three-layer co-extruded rapid bidirectionally stretched wide polyethylene composite film and a preparation method thereof and relates to a polyethylene film and a packaging material. The film comprises three polyethylene film layers orderly comprising a surface layer, a barrier layer and a heat-sealing layer from outside to inside. The surface layer and the heat-sealing layer are prepared from low density polyethylene, metallocene polyethylene, ultrahigh molecular weight polyethylene, a slipping agent and an antistatic agent. The barrier layer is prepared from ethene / vinyl alcohol copolymer resin. The preparation method comprises mother material pretreatment, fusion, plastification and heating of all layers of resin raw materials, filtration for impurity removal, extrusion and flake fluid discharge, cooling to form a glassy casting sheet with uniform thickness on the surface of a cooling roller when the flake fluid flows through the surface of the cooling roller, vertical stretching processes of preheating, drawing and heat treatment setting in a vertical stretching unit, film transverse stretching processes of preheating, drawing, heat treatment setting and cooling in a transverse stretching machine, film traction and rolling for formation of a large coil of a film, and film cutting for finished product formation.