The present invention relates to the technical field of packaging film, and concretely relates to a form-fill- seal (FFS) single layer heavy-duty film and a preparation method thereof. The single layer heavy-duty film is composed of 30-50% of metallocene linear low density polyethylene, 5-20% of an ethylene-vinyl acetate copolymer, 5-20% of ultra low density polyethylene, 20-50% of linear low density polyethylene, and 3-5% of masterbatch, and is obtained via blending in a single screw extruder, and processes of extrusion molding via a machine head, traction, cooling, winding, and printing. Compared with the prior art, the single layer heavy-duty film of the present invention optimizes product formulation, has good tensile strength, impact strength and tear strength; in the preparation process, a gradual cooling mode is adopted, so the resulting product is more stable in performance; and aids are not added in the raw materials, so the product is low in cost and has a good market prospect.