The invention discloses an in-situ synthesized FeSix/diopside complex phase cermet and a preparation method thereof. The complex phase cermet comprises a diopside crystal phase, a glass phase and a metal phase FeSix, wherein the metal phase FeSix is distributed in a continuous matrix phase formed by the diopside and the glass phase. In the preparation method, industrial wastes such as tailings, fly ash, smelting slag and the like which are rich in iron elements are used as main raw materials, and the preparation method comprises the steps of compounding materials, high-temperature smelting, in-situ synthesis, crystallization heat treatment and the like. The FeSix/diopside complex phase cermet is subjected to high-temperature reduction reaction, can not only recover the iron element in industrial waste, but also disperse the nanometer/micron-grade metal phase FeSix in the iron-lean diopside glass ceramic. According to the method, the acid-base corrosion resistance and the toughness of the material are improved, and the industrial application of the glass ceramic is expanded. The glass ceramic has good compactness and high strength, the wear resistance and the impact resistance are good, and can be widely applied to industries such as electric power, chemical industry, coal, steel metallurgy and the like.