The invention discloses a preparation method of nano Cu2O with a flower-like structure and application thereof and belongs to the fields of nano material preparation technologies and catalytic property application. The preparation method comprises the following specific steps: under a room-temperature condition, adopting copper acetate as a main raw material, adding proper amounts of catalyst, reducing agents and protective agents, magnetically stirring and reacting for 45-180 minutes under a room temperature, centrifugally separating suspension liquid, using deionized water to wash for 3-5 times, carrying out air drying at a room temperature to obtain an ideal nano Cu2O with the flower-like structure. The nano Cu2O with the flower-like structure can be used as a catalyst to be applied toreaction of preparing 1H-1,2,3-benzotriazole and derivatives by 1,3-dipolar cycloaddition reaction, has the characteristics of high selectivity and good cycling performance, and shows good catalytic performance. The whole preparation method disclosed by the invention is carried out in a pure water solution system under a room temperature, the experimental operation process is simple, the yield ofa target product is high, the preparation process is stable, the requirements on instruments and equipment are low and the energy-saving and environment-friendly effects are achieved.