n＝2。 To investigate the pyrolysis kinetics process of four samples of biomass (untreated biomass, HCl-washed, 3% KCl-added and 10% KCl-added) of cotton stalks, the experiments were performed by thermogravimetric analysis (TGA) at different heating rates. The results showed the pyrolysis process of these samples could be separated into four stages. With the heating rate increasing, the maximum pyrolysis rate and its corresponding temperature were also increased, and the TG and DTG curves of those samples were shifted to the higher temperature scale. HCl-washed sample was easy to volatilize. For the certain amount of KCl-added biomass sample, the char yield during pyrolysis could be increased. A comparison of the kinetic parameters of 20 sorts of common mechanisms calculated by the methods of Coats-Redfern and Achar with that from the method of Ozawa was made and it inferred that the most possible mechanism functions of untreated biomass pyrolysis is Zhuralev-Lesakin-Tempelman equation, which is a three-dimension diffusion mechanism function; the Avrami-Erofeev equation is more proper for HCl-washed and KCl-added samples, which is a random nucleation and later growth mechanism function, whose reaction order is 2.