The acousto-optic tunable filter (AOTF) is a good prismatic element based on the acousto-optic interaction in anisotropic material. By introducing the working principle of AOTF, the frequency tuning relationship of the applied acoustic frequency in the crystal and the wavelength of the diffracted light is presented, the frequency tuning relationships under different conditions are given, and the function of the birefringence and rotatory property for the TeO2 crystal on the frequency tuning relationship is explained. The regulation how the parameters such as the optical wavelength and the incident polar angle influence the tuning relationship is discussed.