To solve the problem of the degradation of organic pollutants in fracturing flow-back fluid is difficult and the treatment process is complex, the author of this paper had analyzed the mechanism of ultrasonic degradation of hydroxypropyl guar gum, which is a key contaminant in fracturing flow-back fluid. The results suggest that the mechanism of ultrasonic degradation of hydroxypropyl guar gum is mainly physical shearing, ultrasonic mode and power are the main controlling parameters of hydroxypropyl guar gum degradation reaction, followed by concentration. The ultrasonic time, temperature, pH value and other factors have little influence on hydroxypropyl guar gum degradation reaction. For a certain concentration of hydroxypropyl guar gum solution, the optimal degradation parameters are as follows: ultrasonic mode 40%, ultrasonic power 360W, ultrasonic time 60min, temperature 25℃, because of temperature and pH has little influence on hydroxypropyl guar gum degradation reaction, ultrasonic degradation technology can be applied to a wide temperature range (5℃-50℃) and pH range (pH 5.0-11.0).