Abstract: Carbaryl, one of carbamate pesticides, in deionized water, has been studied for its degradation under the radiation of low power ultrasonic bath. Effects of power, frequency, temperature, pH on the ultrasonic degradation of carbaryl has been studied. The result showed that under the experiment condition of 50℃ 、 0.45W/cm 2 、pH6.5, the degradation rate of carbaryl in 135kHz ultrasonic bath was the highest among 28, 40, 50, 135kHz, was about 40.1% after 100min ultrasonic treatment. The degradation rate increased with power, under the experiment condition of 50kHz, 50℃ , pH6.5, the degradation rate of 0.45W/cm 2 was 4.3 times of 0.05W/cm 2 . Under the experiment condition of 50kHz, 0.45W/cm 2 , pH6.5, after ultrasonic treatment for 100min, there are nearly 45% carbaryl degradates and which is about 10 times of the degradation rate under 20℃ . Under the experiment condition of 50kHz, 50℃ , 0.45W/cm 2 , the pH8.0 weak base solution increased the carbaryl degradation rate to 2.8 times of the pH6.5 solution. It was found that the carbaryl degradation process under the ultrasonic radiation were consonant with the apparent pseudo -first -order reaction by the kinetics investigation. The apparent pre -exponential factor increased 40% compared with the original non -ultrasonic condition, the apparent activation energy decreased 9.4% compared with the original non-ultrasonic condition.