The ground state, infrared spectrum and Raman spectrum of the NH3 molecule are optimized using the density functional theory (DFT) B3P86. The excitation characteristics of NH3 molecule are studied by symmetry-adapted cluster/symmetry-adapted cluster-configuration interaction (SAC/SAC-CI) method with basis set D95++. It is shown that the infrared spectral frequency and Raman spectral frequency of NH3 molecule for the ground displacement are completely consistent; vibratory infrared and Raman spectra are active, which are consistent with the theoretical data. A two-dimensional vertical vibration (ν3,5) of infrared intensity is 0.206 km/mol, almost zero, which is related to the excitation characteristics of NH3 molecules. The C3V group becomes D3h group when NH3 molecules are excited from the ground state. This change causes the increases of symmetry and energy. This kind of change doesn′t result in Jahn-Teller effect, but results in the electronic state and dynamic interaction. The electronic state and dynamic interaction are analysed theoretically. It is found that the theoretical analysis is in agreement with the calculated results.