The influences of ultrasonic output intensity, solution pH, H2O2 concentration and the addition of Fenton reagent on the degradation of 2,4-dinitrophenol (DNP) under ultrasonic irradiation were investigated. It was observed that the degradation of DNP fitted pseudo-first-order dynamics under our experimental conditions. Increasing the ultrasonic output intensity increased the degradation efficiency of DNP and low pH favored the ultrasonic degradation of DNP. The addition of H2O2 enhanced the ultrasonic degradation efficiency of DNP. The further addition of Cu2+, however, hindered the degradation of DNP. In contrast, sono-oxidation treatment in combination with FeSO4/H2O2 showed a synergistic effect for DNP degradation.