The invention provides room temperature self-crosslinking water-based paint as well as a preparation method and an application thereof. The paint has high hardness, high scrubbing resistance and good diffuse reflection performance. The preparation method of the paint comprises the following steps: performing graft modification on alkaline silica sol by utilizing a silane coupling agent containing unsaturated double bonds, thereby obtaining nanosilicon dioxide of which the surface is provided with the unsaturated double bonds; by taking the nanosilicon dioxide as a seed, mixing an acrylate monomer and an epoxy resin in the presence of an initiator, and preparing the room temperature self-crosslinking acrylate emulsion which is subjected to epoxy resin and inorganic particle double modification and has a core-shell structure by utilizing a semi-continuous seeded emulsion polymerization process; and by taking the emulsion as a base material, adding a delustering agent, glass powder, body pigment and paint aids, thereby obtaining the room temperature self-crosslinking water-based paint. The paint is coated on the wall surface or board and can be simultaneously taken as a writing board of a doodling pen and a projection screen of a projector, and the problem that the teaching board and the projection screen are independent from each other and cannot be simultaneously used in the prior art is solved.