Abstract: Ultrasonic degradation of chlorinated polypropylene in toluene solution obeyed the kinetic equation：1/(Mt－Mlim)－1/(M0－Mlim)=kt. It was discovered that viscosities of chlorinated polypropylene in dilute solution（1%—5%） decreased with time and finally reached a stable value. Nevertheless，in strong solution（10%—20%），viscosities decreased with time at the initial period and then approached its lowest value. After this lowest value，viscosities increased gradually. The reason why viscosity increased may be that strong solutions became irreversible rheopectic fluids under ultrasonic irradiation. Through determination of infrared spectrum and chlorine content，it was also discovered that the structure and chlorine content of chlorinated polypropylene had no change after ultrasonic irradiation. This indicated that the rupture position of chlorinated polypropylene molecular chain Loated C—C bond.