The influences of hydrochloric acid washing on the pyrolysis behavior and thermodynamic parameters of sweet sorghum stalk were investigated using thermogravimetric analysis and Fourier transform infrared (FTIR) in this study. Hydrochloric acid washing influenced the quality of sweet sorghum stalk and changed the pyrolysis curves shape. By acid pretreatment, the 98% of metals and 47.15% of extractives were removed, the maximum weight loss rates were improved by 1.53-1.64 times, the volatiles yields were enhanced about 10%, and the high heat value increased from 15.59 to 18.27 MJ/kg. Lower activation energies were obtained for acid-washed samples at conversion rate >0.45 by the Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose (KAS) methods. The higher Gibbs free energy of 133.94-137.79 kJ/mol could provide more energy for pretreatment samples, and FFIR analysis confirmed acid washing could change functional groups in samples. (C) 2019 Elsevier Ltd. All rights reserved.