The invention discloses a preparation method of 3,5-difluoroaniline and relates to the technical field of organic synthesis. The preparation method comprises steps as follows: 2,4-difluoroaniline, tap water, hydrochloric acid, bromine, sodium nitrite, sodium monophosphate and ammonium hydroxide are taken as raw materials, cuprous oxide is taken as a catalyst, the tap water and dichloroethane are taken as solvents, and a product of 3,5-difluoroaniline is prepared through steps of bromination, diazotization, ammoniation, extraction, distillation and the like. According to the method, the industrially available raw materials can be utilized for reaction, the process is simple, post-treatment is simple and convenient, conditions are mild, environmental pollution is small, and the product of 3,5-difluoroaniline is prepared with high yield, and meanwhile, industrial production can be realized.