Abstract: In order to investigate the variation law of the reaction rate of the reduction zone during the underground coal gasification process,an independent devel oped fixed bed reactor and the different gasification agents were applied to investigate the coke particle,pressure and flow affected to the gasification of the lump coal. With the variation of the gas contents during the gasification process,the carbonization rate of the coal under different conditions could be calculated. The study results showed that during the coking process of the lump coal,the surface pore of the small particle coke was big and would be more easily gasified. When the flow of the gasi fication agent was 5.6 L 1 min,CO2gasification reaction of the coke would be faster,the flow would be continuously increased and the gasification rate would be reduced. Under different pressures,the coke gasification would have an inflection point and the pressure affected to the density increase of the gasification agents and to the out ward diffusion of the products would have a balance point. Within the pressure of 0 ~ 0. 3 MPa,the gasification rate would be increased with the pressure increased. In t he high pressure zone( pressure over 0.8 MPa),the pressure increased would cause the gasification rate decreased.