Abstract: Through the determination of the angular spectrum of the ultrasonic waves by Fourier transformation, a general formula for calculating the acoustooptic interaction frequency response of AO devices using the first beam steering has been derived. After a full analysis of the effect of the six parameters on the shape of the frequency response curve, a systematic method which determines the values of these six parameters according to the requirements on the shape of the frequency response curve has been proposed. The optimum values of these parameters have been determined for all interested cases on a computer. Thus we completed the optimum design of bulk and thin-film AO devices with planar configuration and two different kinds of step configurations. The results obtained are much better than those published in previous literatures. The accuracy which should be reached for these optimum values in manufacture is also discussed.