A density functional method DFT/B3P86 with relativistic effective core potential basis for U and 6-311+G(d) basis for N is used to study the energy gap and harmonic frequency of UN2 ground state molecule under the action of the uranium-produced spontaneous radiation fields ranging from -0.005 to 0.005 a.u.. The results show that UN2 has an anti-symmetry expansion vibrational frequency ν3 (σg) that is close to experimental value 1051.1 cm-1 under the action of different spontaneous radiation fields, and a symmetrical expansion vibrational frequency ν1(σg) that is close experimental value 1008.3 cm-1. The energy gap is found to decrease with increasing the spontaneous radiation field. The electron which occupies an orbital is easy to excite to empty orbital and transform into an excited state. The UN2 molecule turns unstable in the spontaneous radiation field; N2, O2 and others more easily diffuse into the surface interior, thus corroding the uranium surface and aggravating the corrosion of uranium in the spontaneous radiation field.