Using the density functional method B3LYP with relativistic effective core potential （RECP） for Pu atom, the low-lying excited states （^4Σ^＋, ^6Σ^＋, ^8Σ^＋） for three structures of PuOH molecule were optimized. The results show that the ground state is X^6Σ^＋ of the linear Pu-O-H （C∞v）, its corresponding equilibrium geometry and dissociation energy are RPu-O = 0.20595 nm, RO-H=0.09581 nm and -8.68 eV, respectively. At the same time, two other metastable structures [PuOH （Cs） and H-Pu-O （C∞v）] were found. The analytical potential energy function has also been derived for whole range using the many-body expansion method. This potential energy function represents the considerable topographical features of PuOH molecule in detail, which is adequately accurate in the whole potential surface and can be used for the molecular reaction dynamics research.
