The invention discloses a preparation method of a catalyst for biomass pyrolysis tar steam reforming. The preparation method comprises the following steps: placing and calcining a carrier HZSM-5 zeolite in a muffle furnace in an air atmosphere; sequentially dissolving Ni(NO3)2.6H2O, Mg(NO3)2.6H2O and Ce(NO3)3.6H2O in distilled water to prepare a prepared solution, slowly adding the carrier HZSM-5zeolite into the prepared solution, performing continuous stirring and evaporation to obtain an intermediate mixture, drying and calcining the intermediate mixture to obtain a to-be-reduced catalyst,and reducing the to-be-reduced catalyst to obtain the modified nickel-based catalyst. The catalyst has the advantages of low nickel loading capacity, high catalytic activity, long-term stability and good regeneration performance; the magnesium oxide obviously improves the overall activity of the catalyst and replaces the high nickel loading capacity; and cerium oxide plays a role in reducing carbon deposition of the catalyst. The catalyst is suitable for biomass pyrolysis tar steam reforming.