Based on the analysis of the design theories for non-collinear acousto-optic tunable filter (AOTF) with consideration of the birefringence and the rotatory property of TeO2 crystal, this paper analysed and calculated the angular dependence between the acoustic polar angle θa and the incident light polar angle θi as well as the tuning relation of acoustic frequency fa with the operation wavelength λ0. The calculations show that the approximation for the birefringence and the rotatory property of interaction material leads to an error in the optimum incident angle for TeO2 more than 10%, a diviation in fa-λ0 relation from experiment results, and make the spectral resolution and angular aperture of the device to be degrade. The results abtained will provide a basis for the design of AOTF with large angular aperture.