Abstract: Pyrolysis kinetics of four samples(untreated biomass, HCl-washed, 3% KCl-added and 10% KCl-added) of sweet sorghum bagasse was performed by thermogravimetric analysis(TGA). The results show the pyrolysis process of these samples can be separated into four stages. With the increase of heating rate, the TG and DTG curves of those samples shift up the temperature scale, the maximum pyrolysis rate and its corresponding temperature increase too; the yield of the volatile product is easier for the HCl-washed sample, KCl-added increased the char yield. The mechanism functions of untreated biomass and KCl-added samples pyrolysis accord with Zhuralev-Lesakin-Tempelman equation inferred by the method of Satava, which is a three-dimension diffusion mechanism function, the Valensi equation is more proper for HCl-washed sample, which is a two-dimension diffusion mechanism function.