The present invention provides a safe and non-toxic building waterproof agent, and belongs to the field of building additives. The building waterproof agent of the present invention comprises, by weight, 40-70 parts of an acrylic acid emulsion, 1-5 parts of polyvinyl alcohol amine, 5-10 parts of clay, 5-10 parts of calcium stearate, 2-7 parts of ammonium stearate, 1-5 parts of aluminum stearate, 3-5 parts of calcium fluoride, 1-5 parts of dimethyl silicone oil, 1-2 parts of vinyltrimethoxysilane, 1-2 parts of sodium methyl acryl sulfonate, and 6-20 parts of deionized water. The preparation method comprises: uniformly mixingan an acrylic acid emulsion, polyvinyl alcohol amine, clay, calcium stearate, ammonium stearate, aluminum stearate, calcium fluoride and sodium methyl acryl sulfonate to obtain a mixture, heating to a temperature of 30-50 DEG C, stirring dimethyl silicone oil, vinyltrimethoxysilane and deionized water to obtain a mixed material, and slowly adding the mixed material to the mixture. The building waterproof agent of the present invention has characteristics of inexpensive raw materials, simple preparation method and significant waterproof effect.