The invention provides composite solid-waste lightweight high-strength haydite and a preparation method therefor. The composite solid-waste lightweight high-strength haydite is mainly prepared from the following raw materials in parts by weight: 40.0-60.0 parts of iron tailings, 10.0-15.0 parts of auxiliary raw materials and 0.1-3.0 parts of foamer. The composite solid-waste lightweight high-strength haydite further contains sludge, wherein the dry sludge content of the sludge is 30.0-50.0 parts. The preparation method comprises the steps: accurately weighing the sludge, the iron tailings, the auxiliary raw materials and the foamer according to a designed ingredient proportioning ratio, and carrying out uniform mixing so as to form a uniform basic mixture; and carrying out granulating and shaping so as to obtain unburned haydite, burning the unburned haydite, and carrying out annealing and cooling, thereby obtaining municipal sludge and iron tailing cooperated haydite. The haydite is prepared from the sludge and the iron tailings, which are cooperated with each other and serve as main raw materials, so that the sludge is subjected to harmless treatment and resource-converting utilization, the sludge, which is a municipal mineral product, is used for replacing a primary mineral raw material, and thus the economic and environmental benefits are remarkable.