In the present work, degradation of chitosan with swirling cavitation was investigated to strengthen the effect of degradation, reduce the molecular weight of chitosan and expand the range of application. Different operating parameters such as initial concentration, initial pH, solution temperature, outlet pressure, treatment time and the method of ventilate was investigate on the degradation of chitosan. And different gas such as air, oxygen and nitrogen was used to compare the effect of gas on the effect of cavitation. The results show that: Air has an obvious influence on the degradation of chitosan on the different reaction condition, and the influence of oxygen is better than that of air, but nitrogen is inhibiting the degradation of chitosan. The experiment was performed under the following conditions: a solution concentration of 3 g/L, pH 4.4,a temperature of 60 ℃, a pressure of 0.3 MPa and a treatment time of 3 h, compared with degradation of chitosan in the condition of no-gas swirling cavitation , the aeration of air, oxygen make the intrinsic viscosity reduction rate of chitosan increased by 15.92% and 9.1%.But the aeration of nitrogen make the intrinsic viscosity reduction rate decreased by 9.89%. Therefore, the addition of air and oxygen can improve the degradation rate of chitosan effectively. This study will provide a useful theoretical basis for the development and application of chitosan.