The invention provides a water-based surface treatment agent for the color coating pretreatment of galvanized plates, and belongs to the technical field of the surface treatment of color-coated galvanized plates. The water-based surface treatment agent comprises the following components in percentage by mass: 20 to 60 percent of water-based resin, 1 to 5 percent of organosilane, 0.5 to 2.5 percent of inorganic corrosion inhibitor, 0.5 to 3 percent of sealant, 1 to 3 percent of accelerating agent and the balance of deionized water. In the water-based surface treatment agent, the inorganic corrosion inhibitor, nano particles, the organosilane and the water-based resin are combined organically to form a composite passivating film, so the bonding force of the passivating film and a galvanizedlayer is improved, and the coating performance of the galvanized plate subjected to the surface treatment is improved. Nano-silicon dioxide serving as the sealant can be distributed in the passivating film uniformly after being modified to improve the compactness of a film layer, so the decay resistance of the film layer is improved. The water-based surface treatment agent does not contain chromium with any valence state, and is environmentally-friendly, the pretreatment process is simple, and the requirement of a color coating process can be met.