The invention discloses a polymerization method used for reducing vinyl chloride/vinyl acetate copolymer blending resin glass transition temperature. The polymerization method comprises following steps: vinyl chloride monomer, vinyl acetate monomer, a dispersing agent, a size stabilization agent, an initiating agent, and desalted water are delivered into a polymerization kettle for reaction; temperature is increased to 48 to 52, and is maintained for 1 to 2h, and then is increased naturally to 60 to 65 DEG C; when reaction pressure is reduced to 200 to 300KPa, a terminating agent and an antifoaming agent are added to end the reaction so as to obtain a vinyl chloride/vinyl acetate copolymer blending resin slurry emulsion; an alkaline liquor is added, and the vinyl chloride/vinyl acetate copolymer blending resin is collected from a reaction product. According to the polymerization method, the vinyl chloride/vinyl acetate copolymer blending resin is relatively low in glass transition temperature Tg, excellent in fluidity, flexibility, toughness, and thermoplasticity, is convenient to process, can be adhered with metal surfaces easily, and can be widely used for preparing plastic floor, transparent packaging sheets, artificial leather, protective paint, magnetic binders, and printing plates.