Abstract: In order to optimize the process conditions of U(Ⅳ) produced by N₂H₄ reducing U(Ⅵ) with platinum as catalyst in the nitric acid environment, determine the control steps of the reaction process, improve the rate of controlling step in the reaction, and determine the reaction path and reaction mechanism, it is necessary to confirm the manner of bond breaking and decomposition mechanism of the N₂H₄ with Pt as catalyst. In order to determine the bond breaking mechanism of N₂H₄ in this process, gas chromatography, spectrophotometry, titration and drainage method were used in this paper to analyze the product in the process of U(Ⅳ) produced by N₂H₄ reducing U(Ⅵ) with Pt as catalyst in the nitric acid environment. The results show that there is no hydrazoic acid, nitrogen oxides or hydrogen product in the process. The main product is N₂, and the consumption ratio of N₂ to N₂H₄ is close to 1∶1. When there is U(Ⅵ), the yield of NH⁺₄ is low, and the production rate of NH⁺₄ increases sharply when the U(Ⅵ) reaction is complete. N—N bond breaking and N—H bond breaking coexist. Increasing temperature is conducive to speed up the reduction reaction.