The invention discloses a preparation method of a carbon dot hybridization mesoporous nickel boride photocatalyst. According to the method, the carbon dot hybridization mesoporous nickel boride photocatalyst is prepared by the steps of citric acid solution preparation, nickel addition, hydrothermal reaction, pH (potential of hydrogen) value adjustment, sodium borohydride addition reaction and centrifugation. The preparation method of the carbon dot hybridization mesoporous nickel boride photocatalyst has the advantages of simple process, easiness in control, high yield and the like.