The distribution of base mode Gaussian beam′s electric field through LiNbO3 deflector is calculated based on the beam refraction theory in the media interface and the vectorial theory of propagation in anisotropic media.The model of the intermediate frequency current, from the detector of beam orienting system, versus beam mismatched angle is rebuilt.The computer simulation results demonstrate the effect of output electric field change on the intermediate frequency current as a function of mismatched angle.High beam orienting precision can be obtained based on the revised mathematical model.