In this present work, the pore structure of Gonglangtou oil shale, and of its five char samples prepared at air atmosphere and 850 degrees C, is measured by applying N-2 adsorption-desorption method. On the basis of the measurement results and the combustion mechanism of oil shale, the evolution mechanism of pore structure during combustion is discussed. At high heating rates, kerogen decomposition makes pore volume and specific surface area decrease in the preignition stage and then largely increase in the main combustion stage; in the burnout stage, the pore volume and specific surface area decrease again, because of oil-shale-ash melting deformation, which results from the absorption of heat from oil shale combustion and ambient heat transfer. In addition, the oil-shale-ash melting deformation in the burnout stage also makes pore shape shift from slitlike to heterogeneous and makes pore-size distribution uniform. For improving the combustion efficiency of oil shale-fired devices, particle size should be decreased in order to increase the pore volume and the specific surface area, besides that the residence time of oil shale in combustion devices is lengthened.