Abstract: The typical azo dyes acid orangeⅡ(AO7),which contains several benzenes,has been investigated under the irradiation of ultrasound and ultravioletlight respectively and simultaneously.It is found that the degradation of AO7 in solution occurs under the irradiation of ultrasound or ultraviolet,in which the reaction process for the AO7 degradation shows a pseudo-first order kinetics.The same reaction kinetics is found for the degradation of AO7 under the combined ultrasound and ultraviolet.We further have found that the degradation efficiency for AO7 under the combined irradiation of ultrasound and ultraviolet is larger than the sum of that under the respective irradiations of ultrasound and ultraviolet light,indicating a synergistic effect of ultrasound and ultraviolet light irradiations.Based on the analysis of the reaction kinetics,the synergistic effect could be ascribed to the ultraviolet induced decomposition of hydrogen peroxide (H₂O₂).