Single beam laser irradiation by acoustooptic medium under the effect of a single ultrasound source causes the Bragg diffraction phenomenon. Considering of acoustooptic effect under multiple ultrasonic beams,the investigation was focused on the influence to acoustooptic effect with the changing of source signal under multiple ultrasonic beams.The relationship between stress caused by ultrasonic waves and refractivity of medium was derived by Maxwell equations. The stress distribution and the light path simulation were proved by MATLAB. Result showed this acoustooptic medium had the characteristics of optic crystal.