On the basis of Hamiltonian derived in the references <参考文献原文>under the dipole and rotating-wave approximations, the energy spectrum of ionic-crystal lattice vibration anharmonicly in lightfield is discussed. The energy level as the total number n of photons and optic phonons with the same mode-frequency splits up into sublevels via the photon-phonon and phonon-phonon coupling, which would be a kind of dynamical (A.C.) Stark effect. We found a purely quantum effect: the n=0 (vacuum) level is shifted by the interaction between phonons themselfs. It is expected that spectrum calculated might be another resource of information for crystal structure.