Abstract: In a study of the photochemical reduction of uranium (Ⅵ) to produce uranium (Ⅳ) in the organic phase of TBP, a high pressure mercury lamp is chosen as the exciting light, and CC14 is used as the diluent for TBP. The effects of factors such as reaction temperature and the composition of initial aqueous phase solution etc, on the yields of uranium (Ⅳ) and nitrous acid is investigated. The optimum condition for producing uranium is recommended.