Abstract: Shengli brown coal was gasified at 800-900℃ in a simulated entrained-flow reactor, φ 80×3 000 mm.The physical structure and functional groups of char were tested by infrared spectroscopy, X-ray photoelectron spectroscopy and Raman spectroscopy while coal gas was tested by gas on-line analysis instrument in order to explore the mechanism of promoting effect of oxidation reaction on steam gasification reaction.The results show that the synergy effects can be explained by dissociated adsorption reaction mechanisms of steam gasification reaction and semi-coke pore structure features under different atmospheres.The oxidation reaction can make microspores number, specific surface area, pore volume and adsorption capacity of the char particles greatly increase and more carbon active sites expose by producing microspores, developing mesopores;it also prompts small groups as-CH₃, -CH₂-, ＞ C=O & ＞ C-O-fractured and generation of hydrogen free-radical and carboxyl.All these promote steam gasification reaction rate, especially at a higher water vapor content or temperature.Meanwhile, the oxidation reaction can change the relative content of CO₂, CO, H₂ and internal energy of steam molecules and activated carbon atoms, in favor of steam gasification reaction.