This study aimed to explore the combustion kinetics of organic matter in Huadian oil shale using thermogravimetric analysis. Increases in particle size or heating rate shifted the combustion process to a higher temperature, because of mass transfer resistance and thermal hysteresis. An investigation into activation energy using the Coats and Redfern, Starink, and Flynn-Wall-Ozawa methods indicated that oil shale combustion process is controlled by multiple reaction mechanisms. Therefore, multi-stage parallel reaction model and bi-Gaussian distribution function were introduced into the analysis of this complex combustion process. A four-stage parallel reaction model for bitumen, volatiles in kerogen, macromolecules and non-volatiles in kerogen, and fixed carbon was used to characterize the combustion process of organic matter in oil shale. The activation energies showed an increasing trend for the four sub-stages. The mechanism of each sub-stage established by Malek's method showed that the second and third sub-stages of the kerogen combustion proceeded via chemical reaction mechanisms and the 3D Zhuravlev-Lesokin-Tempelman model regardless of particle size and heating rate. This finding revealed the intrinsic reactivity and thermal stability of kerogen combustion. (C) 2015 Elsevier Ltd. All rights reserved.