The acousto-optic tunable filter (AOTF) is one kind of fast tunable prismatic elements based on acousto-optic interaction in anisotropic material. The wavelength of the output light can be tuned fastly and flexibly by changing the frequency of the applied acoustic wave. The spectral resolution is one of the main indice for evaluating the performance of AOTF. The TeO2 based noncollinear AOTF is selected as an object. From the basic theory of acoustic-optic interaction, the equation of the spectral resolution is deduced systematically, and the related factors are analyzed. The relationship of the essence property of TeO2 material (particularly the rotatory property of TeO2) and the spectral resolution is discussed.