This paper deals with the intracavity interaction of lightfield with anharmonic lattice vibration of ionic crystal. The nonlinear lattice dynamics and an expression of nonlinear macroscopic polarization are derived in terms of optic phonon modes. Under rotating wave approximation, the total coherent Hamiltonian of photon-phonon coupling system driven by incident field is introduced. By the corresponding equations of steady state, the increasing absorption optical bistability (IAOB), as a nonlinear effect, is demonstrated. The results show that the nonlinear interaction of light field with various elementary excitations of boson type, such as photon and exciton, may be served as a mechanism for IAOB.