The invention discloses a preparation method of a biomass tar cracking catalyst. The catalyst is prepared from raw materials including iron oxide nanoparticles, octadecyl triethoxysilane, high-carbonorganic matter, rice husk, sodium metaaluminate, nickel nitrate and the like. An iron oxide magnetic material is inserted in preparation of the catalyst, recovery and reuse of the catalyst are facilitated, deposed carbon is diffused and mixed horizontally through combustion of the high-carbon organic matter, doping is more uniform and ordered, more catalytic active sites and adsorption sites can be reserved, meanwhile, mayenite is prepared to be compounded with a nickel-based catalyst, the carbon deposition resistance of the nickel-based catalyst is improved by use of free oxygen structures, the catalytic performance is enhanced, and efficient degradation of biomass tar is realized. The raw material source is wide, the preparation method is simple and high in applicability, the stability of the biomass gasification process can be substantially improved, the gasification cost can be reduced, and the method has higher economic value and environmental value and is suitable to be promotedand used by manufacturers.