The invention provides a preparation method of a biomass gasified tar cracking composite catalyst, comprising the following steps: first, the preparation of a binder: Ni(NO3)2.6H2O crystal and Al2O3 powder are weighed, the Al2O3 powder is added in the water solution of the Ni(NO3)2.6H2O crystal, immersed for 2h-4h at constant temperature water bath of 40 DEG C, dried into light green powder and calcinated; second, the pretreatment of dolomite: the dolomite is ground into powder of 200 meshes below; third, the preparation of a carrier of the composite catalyst: Fe2O3 and the dolomite powder are mixed uniformly and are added with the binder and 5-20mL of nitric acid to be mixed +-<*> uniformly, and the mixture is extruded to be molded, dried naturally, dried at 105 DGE C, calcinated under 400 DEG C and then calcinated at 900 DEG C; forth, the solution immersion of active components: Ni(NO3)2 ethanol solution is used for immersing the carrier of the composite catalyst, and after dried, the carrier is calcinated at 600-800 DGE C. the composite catalyst has the advantages of high catalytic activity, good strength, practical application and simple process.