Abstract: In order to study the effect of O2/CO2 as gasification agent in underground coal gasification (UCG)，temperature field, gas composition and pollution emi ssion were contrasted in two ways of O2/CO2 and O2/Air gasification experiment on a model test of UCG plant, at the same time, CO2 emission reduction were calculat ed for O2/CO2 gasification. The result shows that high content of CO2 will extend the gasification time and make the temperature field be distributed along the axial wa y; the gasification rate and temperature change is nearly the same when the content of 02 is 60% in two ways, and the heat value of gas is extremely high in the O2/CO 2gasification; it is calculated that CO2 emission reduction can reach the biggest value for O2/CO2 gasification when 02 content is 40%, and the number of coal-burning will reduced by 40% than O2/Air gasification. The emission of H2 S and NH3 can be scientifically decreased in O2/CO2 gasification than that of O2/Air gasification.