The invention relates to an autoclaved aerated concrete building block and a preparation method thereof, in particular to an autoclaved aerated concrete building block containing industrial solid waste and a preparation method thereof. The autoclaved aerated concrete building block containing industrial solid waste comprises, by weight percent, 35%-47% of base material, 35%-39% of magnesium chloride solution, 10%-15% of magnesium oxide, 2%-5% of binder, 2%-3% of industrial hydrogen peroxide, 1%-2% of lanthanide rare earth, and 5%-7% of additive. The autoclaved aerated concrete building block has the advantages of fire prevention, water proofing, moth prevention, lightness, crush resistance, bending resistance, high strength, moss avoidance and the like. The proportion of the materials determines the water proofing and moth prevention. The fire prevention meets the standard (class A) of nonflammable materials. The crush resistance is larger than 53Mpa. The bending resistance is larger than 80Mpa. In addition, the industrial solid waste is effectively utilized, wastes are utilized, environment is protected, and the wastes are turned into wealth.