Abstract: Molecular weights of chlorinated polypropylene at various concentrations under ultrasonic irradiation were measured.Limiting molecular weight of polymers under ultrasonic irradiation could be(obtained) by data fitting technique.Siwe the fitting accuracy of the common kinetic equations of polymers under ultrasonic irradiation for experimental data was evaluated.The fitting results of these kinetic equations for experimental data are not satisfactory,in order to establish the kinetic equation for chlorinated polypropylene in toluene accurately,an improved kinetic equation for ultrasonic degradation was proposed in this article: 1M_(t)-M_(lim)1M_(0)-M_(lim)=kt.It describes well the ultrasonic degradation grocess of chlorinated polypropylene.The fitting effect for some experimental data in literature using the new equation is better than that of the kinetic equations used in literature.For chlorinated polypropylene under ultrasonic irradiation,the rate coefficients decrease with increasing concentration and the limiting molecular weights increase with increasing concentration.