Abstract: In order to obtain the accurate design parameters of acousto-electro-optic (AEO) devices, the geometrical relationships of anomalous acousto-optic effect are studied by tangent condition and matching condition. Angle relationships of incident light vector, diffractive light vector and optic wave vector are determined. Curves of extreme frequency and acousto-optical (AO) merit for different ultrasonic waves in xOz plane are systematically given. Further on, the design parameters under different central frequency are also calculated. The results show that parameters gained by this way are more precise comparing to that gained by solving Dixon equations.