The invention discloses a vinyl chloride copolymer emulsion for water-based anticorrosion coatings and a preparation method thereof, comprising the steps of: adding deionized water, vinyl chloride, allyl chloride, isobutyl vinyl ether, maleic anhydride, Emulsifier and reducing agent, stir and heat up to 45-60°C, then continuously drop ammonium persulfate initiator aqueous solution to start polymerization, continuously add vinyl chloride during polymerization, control the speed of vinyl chloride addition, and maintain the pressure of the polymerization system ± 0.1 kg / cm 2 , continue to polymerize until the pressure of the system drops by 0.5-2.0kg / cm after adding vinyl chloride 2 When the temperature is lowered, the polymerization is terminated, unreacted monomers are removed, and a vinyl chloride copolymer emulsion is obtained. The present invention increases the chlorine content of the copolymer by introducing the addition amount of propylene chloride monomer and isobutyl vinyl ether, and at the same time introduces maleic anhydride, the caking monomer, so that the obtained vinyl chloride copolymer can be used to prepare the vinyl chloride copolymer with good anticorrosion effect and Adhesive water-based paint.