The invention belongs to the technical field of preparation of nano-catalytic materials and relates to a preparation method of a nano-copper oxide catalyst for degrading organic dye wastewater. The method comprises the following steps: 1) dissolving a strong base in hydrogen peroxide to prepare a strong base mixed solution, adding a copper ion solution with the concentration of 0.8-1.2mol/L into the strong base mixed solution while stirring, continuing stirring, centrifuging to obtain a precipitate, and washing with water; 2) dispersing the precipitate in deionized water to obtain a suspension, performing sealed aging treatment on the suspension at the temperature of 60 DEG C-100 DEG C for above 4h, then cooling, washing with deionized water and ethanol, and further drying to obtain the nano-copper oxide catalyst. According to the method provided by the invention, the advance preparation of a template and the use of any surfactant are not required, the method has the advantages of mild reaction, simple process, short period and no pollution of raw materials and products, and the prepared nano-copper oxide catalyst has the advantages of regular shape, uniform particle size and good catalytic performance.