The invention belongs to the technical field of coatings, and particularly relates to a water-based coating for backing of packaging paper before printing and a preparation method of the coating. The coating comprises the following raw materials: deionized water, alcohol, a styrene copolymer, acrylic resin and an auxiliary agent, wherein the styrene copolymer is obtained by polymerizing styrene and at least one monomer selected from the group consisting of butyl acrylate, methyl methacrylate, isooctyl acrylate, methacrylic acid, polyester acrylate and glycidyl methacrylate, and preparation monomers of the acrylic resin comprise butyl acrylate, methyl methacrylate, isooctyl acrylate, methacrylic acid, polyester acrylate and glycidyl methacrylate. The coating provided by the invention does not contain substances toxic to human bodies, such as benzene and methanol, has the advantages of good printing adaptability, good adhesion fastness, high surface brightness of a coating film and friction resistance, and is suitable for printing of paper products with high environmentally-friendly requirements, such as tobacco, wine, cosmetics and daily necessities.