The invention relates to a method for preparing sintering-expanded haydite from magnetically separated copper slag and flyash. The method comprises the following steps: carrying out drying and fine grinding treatment on sintering-expanded raw materials, and then mixing the raw materials in proportion to obtain a sintering-expanded haydite base material; carrying out forming treatment on the sintering-expanded haydite base material to obtain haydite pellets; drying the haydite pellets to obtain dry pellets; and roasting the dry pellets to obtain the sintering-expanded haydite. The magneticallyseparated copper slag and the flyash are used as main raw materials, the sintering-expanded haydite is prepared by raw material proportioning and a production process, because the magnetically separated copper slag contains a certain amount of ferric oxide and carbon residues, the gas evolution of the magnetically separated copper slag is high, in a production process, the calcination temperatureis low, the expansion rate of the haydite is high, the magnetically separated copper slag which is stored for a long time is utilized, the cost of raw materials is low, and meanwhile, energy consumption in a production process is reduced. The prepared sintering-expanded haydite is low in density and high in strength, and can meet requirements for light concrete l aggregates.