The invention belongs to the technical field of building wall materials, and particularly relates to autoclaved aerated concrete containing coal gangue and iron tailings and a preparation method of the autoclaved aerated concrete. The autoclaved aerated concrete containing the coal gangue and the iron tailings is prepared from the following raw materials in parts by weight: 5 to 30 parts of the coal gangue, 15 to 25 parts of aluminum slag, 30 to 55 parts of the iron tailings, 5 to 15 parts of nanoscale silicon dioxide, 5 to 15 parts of metakaolin, 10 to 15 parts of quick lime, 0 to 5 parts of cement and the balance of waste materials. Auxiliary materials include aluminum powder, a foam stabilizer and a water reducing agent. In the raw materials, the iron tailings and the coal gangue are used as siliceous materials, so that the environmental problem caused by solid waste stockpiling can be solved, waste is turned into wealth, and meanwhile, a good effect is achieved on the sustainable development of the society. The prepared concrete block has good physical and mechanical properties and durability, the product performance meets the national standard requirement, and 04-grade, 05-grade, 06-grade and 07-grade concrete blocks can be produced according to different proportions and process systems.