Abstract: In the underground fire zone,high temperature coexists with inert gases after inert injection,and the O2 con- centration remains a lower level. Spontaneous combustion characteristics of coal are partially changed by the joint effect of temperature and inert gases such as CO2 or N2 . Taking the Qingdong bituminous as an example,the coal sample was pretreated for 24 h at an inert or low-oxygen environment ( CO2 ,N2 ,10% O2 ) under 200 ℃ . The physicochemical properties of coal were analyzed according to the FTIR,pore analysis and TG test. Oxidation products were compared via the temperature-programmed experiments. The results show that after treatment the coal is easier to self-ignition. Its activation energy decreases,but the critical temperature increases. Besides,the proportion of mesopores and macropores increase,and the permeability and porosity of coal also rose significantly. In addition,the C O and C—O functional groups increase,while the —OH and heteroatomic groups in coal decrease. Further,various types of connected cracks and porosities are generated,which enhance the gas flow in coal.