The equilibrium geometries for the ground state of PH2 radical are calculated by using the coupled_cluster single_double model with a perturbative triple excitations （CCSD（T）） method in combination with the series of correlation-consistent basis sets of Dunning and co-workers. It can be found that the cc-pV5Z basis set is the most suitable basis set by comparing the calculations with the experiment. The results obtained at CCSD（T）/ cc-pV5Z level of theory are 0.14185 nm for the equilibrium bond length RP—H, 91.8624° for the bond angle αHPH, 3.483 eV for the dissociation energy De and 2399.9781, 1128.4213 and 2407.8374 cm-1 for the normal of vibrational frequencies（ν（a1）, ν2（a1） and ν3（b2）, respectively. The potential energy function of PH2 （C2v, X2B1） is derived using many-body expansion theory. The characters of structure and the change of energy are reflected correctly by the function.