Abstract: We present a theory of ultrasonic gelleration via direct interaction of transverse optic (TO) phonons withphotons in anharmonic lattice of ionic crystals.There are two methods of supplying light energy for the excitation of TOlattice wave as a high frequency ultrasound:(1) incident light comes from the source outside the cavity fulfilled withionic crystal medium;(2) photon mode of the cavity possesses the gain of amplilication by stimulated radiation of activeatoms doping in the medium.More attelltion is drawn to the case (2).The working system of case (2),as a mixture oflasing action and ultrasonic generation,has the threshold phenomena like usual laser.And the linear stability analysisshows that the nonlinear phonon-photon coupling and the interaction among phonons themselves,both of which reflectthe anharmonicity of lattice vibration,are necessary to the stable ultrasonic output.So this laser-ultrasonic generationmixture would be also a measure to investigate the lattice-dynamic nonlinearity and correlated electromagnetic propertiesof ionic crvstals.