There is a high demand for a computational model that calculates effectively the phase and amplitude distribution of the beams emerging from an acousto-optic cell. We present a model based on a new algorithm that is capable to solve the vectorial optical wave equation on consecutive planes in an optically anisotropic medium with an arbitrary refractive index distribution with limited refractive index amplitude. Strength of the presented method is that it does not require the paraxial approximation. We used the model successfully to calculate the amplitude and phase distribution of the diffracted and undiffracted beams generated in optically anisotropic and isotropic acousto-optic interaction.