According to the actual practical condition of acousto-optical deflectors, by solving Dixon equations of abnormal Bragg diffraction under the condition of fixed incident light direction ?1, the functional dependences of the ultrasonic wave direction ?a. which gave rise the acousto-optical interaction and the diffraction light direction ?2 on the frequency f are obtained. From the ?a-f relationship, the important design parameters, i.e., the Bragg bandwidth and the transducer length, can be determined accurately. The ?2-f relationship shows good linearity, hence the previously proposed corrections on scanning linearity appear to be unnecessary.