The invention discloses a sand-in-sand multicolor interior and exterior wall building coating material and a preparation method thereof, and relates to the field of building coating materials, whereinthe components of the formula comprise: a granulating agent, cellulose, a pH value regulator, a bactericide, inorganic bentonite, an anti-freezing agent, a film forming aid, a granulating emulsion, sand, an emulsion, a dispersing agent and titanium dioxide. The preparation method comprises: preparing a white base paint, preparing a granulating agent system, granulating, preparing a real stone paint and preparing a finished product. According to the invention, based on the sand-in-water multicolor coating material, through the specially-made granulating agent adding and the process, the sand-in-water color particles have characteristics of low use amount of, various colors, stone-like fidelity and the like, the real stone paint has advantages of favorable constructability, high storage stability and favorable texture effect, and the sand-in-water color particles and the real stone paint are combined to form the completely-new sand-in-sand multicolor coating material, so that the existing technical difficulties are solved, and the existing comprehensive advantages are retained.