The deviation caused by acousto-optic tunable filter (AOTF) diffraction in multispectral imaging is analyzed through derivation calculus of the deviation angle. The rotatory polarization of acousto-optic crystal is taken into account in this analysis. The relationships between the polar angle of the incident and the diffracted beams are acquired by using the momentum-matching condition. During the diffraction of the incident beams, far more deviations are induced.