The invention discloses a method for preparing a SiC-based multiphase ceramic solidified body, which is characterized in that the steps are: using ZnO, CaO, Al 2 o 3 , SiO 2 As a raw material, ZCAS glass is obtained by ball milling, drying, calcining, ball milling, and drying; SiC-ZCAS composite powder is obtained by ball milling, drying, and calcining using silicon powder, graphite, and ZCAS glass as raw materials; Adding polyvinyl alcohol sol, mixing, granulating, and pressing to shape; heat-treating the shaped green body and sintering it in a vacuum hot-pressing sintering furnace to obtain a SiC-based multiphase ceramic solidified body. The invention adopts safe and cheap raw materials, simple and practical vacuum hot pressing sintering technology, and prepares a SiC-based multiphase ceramic solidified body with excellent radiation resistance stability, chemical stability, mechanical stability and thermal stability at a relatively low temperature. The SiC-based multiphase ceramic solidified body prepared by the invention is suitable for safe treatment of high-radioactive graphite waste produced by decommissioning of nuclear reactors.