Abstract: The density functional method DFT/B3P86 with relativistic effective core potential basis for U and 6-311+G(d) basis for N was used to study the energy gap, harmonic frequency, and Fermi energy level of ground state UN molecule under different inner radiation fields ranging from -0.005 to 0.005 a.u. The results show that the harmonic frequency is close to experimental value 1 007.7 cm^-1 under different inner radiation fields. The energy gap and Fermi energy level are found to increase with the inner radiation field. The electron of occupied orbital is difficult to stimulate to empty orbital and to transform into excited station. The UN molecular is more stable in inner radiation field, so it can prevent N₂ and so on to proliferate to superficial inner layer and then corrode the uranium surface, which contributes to the uranium corrosion prevention in inner radiation field.