The invention discloses a method for preparing a tar pyrolysis catalyst by utilizing a waste SCR denitration catalyst. With the waste SCR denitration catalyst as an active metal source, the waste SCRdenitration catalyst is placed in mixed acid of nitric acid and hydrofluoric acid for high-temperature decomposition to obtain a decomposition solution containing active metal, the decomposition solution is dipped on a carbon material for obtaining a precursor and calcined in a mixed atmosphere of CO2 and/or H2O and inert gas at 650-800 DEG C, and the high-activity tar pyrolysis catalyst is prepared. The tar pyrolysis catalyst is used for treating tar formed through pyrolysis of carbon-containing substances such as coal and biomass fuel, polycyclic aromatic hydrocarbon and the like in the tarcan be further subjected to catalytic pyrolysis for forming light aromatic hydrocarbons such as benzene and methylbenzene, the highest increasing rate of the light aromatic hydrocarbons can reach 430%, light conversion of the tar is achieved, and accordingly the quality of the tart is improved.