Abstract: In this paper, with natural high molecular weight chitosan as raw materials, ultrasonic degradation is used to prepare oligochitosan.Single factor experiment is performed to study the effect of hydrochloric acid quality score, degradation temperature, ultrasonic power and ultrasonic time on the ultrasonic degradation of chitosan.the optimal degradation preparation conditions of the molecular weight chitosan less than one million are determined by the orthogonal experimental design.Resultsshow that the best degradation conditions of ultrasonic degradation of chitosan are 3% concentration of hydrochloric acid, the degradation temperature of 65℃, ultrasonic power 500W, and ultrasonic time of 180min.In the best degradation condition, the oligochitosan with 6869 molecular weight can be available.