Abstract: The bio-char from cotton stalk and sawdust was prepared using a tubular fixed bed, and the combustion characteristics of the resulted bio-chars were analyzed with a thermogravimetric analyzer. Based on the comprehensive reaction rate equation, the gas-solid reaction mechanism of the bio-char combustion was deduced, and the thermogravimetric data of the bio-char combustion were fitted. The results indicate that as the carbonization temperature increases, the ignition temperature and burnout temperature of the bio-chars increase, while the combustion performance index (S) decreases. The combustion characteristics of the cotton stalk charcoal are better than that of the sawdust charcoal. The reaction mechanisms for the cotton stalk charcoal combustion are different in different temperature ranges. The charcoal combustion in lower temperature range follows the planar internal diffusion reaction mechanism, while the globular interface reaction mechanism applies to higher temperature range. The combustion reaction of sawdust charcoal follows globular interface reaction mechanism during the whole oxidation process. The reaction reactivity of bio-char combustion can't be judged by the calculated activation energy.