The invention discloses a water-based plastic coating. The water-based plastic coating comprises the following components: a water-based resin emulsion, deionized water, a filler and additives. The invention further designs a preparation method of the water-based plastic coating, and the preparation method comprises the following steps: adding the filler into the water-based resin emulsion, adding an appropriate amount of deionized water, stirring, pouring into a sand mill for grinding, putting into a dispersing cylinder when the fineness is below 80mu m, adding the additives, sealing, stirring and detecting the viscosity for not less than 95s to prepare the water-based plastic coating. The water-based plastic coating has excellent water absorption, water retention, water suction and drainage and a good humidity adjusting effect, can be used for regulating the indoor relative humidity, and has the advantages of relatively high scrubbing resistance, water resistance and solvent resistance, corrosion resistance, alkali resistance, light resistance, weather resistance, good film-forming property, excellent color retention, wear resistance, corrosion resistance, controllable hardness, high performance-price ratio and the like, and the preparation method is simple, easy to operate without pollution, good in construction and safe to use.