The invention discloses a method for preparing aerated concrete from gangue and iron tailings. The method comprises the following steps of crushing non-hypergolic raw gangue to obtain particles of -2mm, carrying out drying, mixing 20-30% by mass of the gangue, 30-45% by mass of iron tailings, 22-30% by mass of carbide slag and 3-8% by mass of flue gas desulfurization gypsum to obtain a uniform mixture, wherein the above four raw materials are mixed according to mass percents after calcination, milling the mixture to powder with a specific surface area of 310-400m<2>/kg, calcining the powder at a temperature of 750-850 DEG C for 2-3h, naturally cooling the powder, adding the cooled powder into cement according to a ratio of 1: 0.03-0.07, and based on the total weight of the dry material, adding 0.05-0.06% of aluminum powder paste, 57-62% of warm water and 0.025-0.026% of a foam stabilizer into the mixture. Through pouring, standing maintenance, blank cutting and autoclaved curing, the aerated concrete accepted product with oven dry compressive strength of 3.5MPa or more and oven dry volume density of 550-625kg/m<3> is obtained.