The invention relates to the technical field of metal surface treatment, in particular to a preparation method of a water-based metal cleanser. A novel environment-friendly water-based anti-rust agentis prepared by modifying a styrene-acrylic emulsion with polyvinyl alcohol and taking the styrene-acrylic emulsion as a primary film forming substance based on main monomers of methyl methacrylate, methyl acrylate and acrylic acid. Nano gelatin particles are also added at the same time. As the nanoscale particles are large in size, large in specific area, high in surface energy, atoms on the surface are great in proportion and high in activity, and effective functional groups are available, so that the nano solution coated to the surface of a metal can be tightly combined with the surface ofthe metal, and the film layer is compact; some active radials are also exposed in air to be in contact with the external environment to be rusted, so that as an anti-rust film is combined out of thenano film layer, the surface area of the anti-rust film is increased, the active radicals are combined with the anti-rust film, and therefore, the adhesive force and the surface hardness of the antirust agent film layer are improved effectively, and the anti-rust performance of the cleanser is improved.