The invention provides a preparation method of a high-efficiency ozone catalyst and a method for treating coal-gasification wastewater. An aluminium oxide ball is adopted as a carrier to be fully impregnated in a Cu (NO3) 2 solution for 12-36 hours, and then dried and calcinated to finally obtain the CuO/Al2O3 catalyst; in the catalyst, the mass fraction of Cu elements is 2-3.5%. The prepared catalyst has high catalytic efficiency, simple technological process and low reaction energy consumption.