The invention relates to the technical field of coatings for casting sand molds, in particular to a water-based dip coating for a 3D printing sand mold and a preparation method thereof. The water-based dip coating for the 3D printing sand mold is prepared from the following components, by mass: 50-75% of composite refractory aggregate, 3-6% of a composite suspending agent, 0.8-1.2% of a compositebinder, 0.1-0.5% of a penetrating agent, 0.2-0.6% of a leveling agent, 0.05-0.2% of a preservative, 2-5% of a fluxing agent, 0.1-0.3% of a defoaming agent and the balance water, and is characterized in that the composite refractory aggregate is formed by mixing one or a mixture of zircon powder, spodumene powder and carborundum powder with spinel powder according to the mass ratio of 50:(4.5-16.5), wherein the spinel powder is magnesium aluminate spinel powder, magnesium-chromium spinel powder or aluminum-chromium spinel powder, and the particle size of each component is 320-600 meshes. The water-based dip coating has the advantages of being excellent in coating performance, proper in permeability, good in leveling property, efficient in suspension stability, proper in coating thickness, good in sintering stripping property and super-strong in anti-sand-burning property.