The gasification reaction efficiency of coal in the gasification channel is a key issue affecting the gas composition and calorificvalue of underground coal gasification. To reveal the effects of reaction temperature and pressure on the gasification behavior and productdistribution characteristics of lignite in water vapor using the coal deposited in the Santanghu Basin, pyrolysis experiments were carried outusing lignite collected from the Xishanyao Formation of the Santanghu Basin based on a fixed-bed pyrolysis furnace under different reactiontemperatures and pressures. With the increase of reaction temperature (300-900 ℃ ), the gas mass fraction increased from 3.84% to24.29%, and the mass fractions of water and tar increased first and then decreased. The volume of H2 and CH4 increased significantly withthe increase of reaction temperature, with the maximum volume of 100.89 and 106.09 mL/ g at 900 ℃ , respectively. The total mass of pollutants decreases, and the mass is relatively small at 900 ℃ , 17.72 mg/ g. Increasing the reaction pressure (1.5-3.0 MPa) is beneficialto improve the conversion of semi-coke and increase the gas mass fraction. The increase of reaction pressure aggravates the secondary reaction, which is conducive to the occurrence of hydrogasification reaction and methanation reaction, resulting in a significant increase in thevolume of CH4. At 700 ℃ , the volume of CH4 increases by up to 26.89 mL/ g. However at 700 ℃ , the free radical hydrogenation saturation reaction is promoted, resulting in an increase in the total mass of pollutants. It is suggested that in the actual production, the reactiontemperature and pressure should be increased by controlling the moving speed of steam injection, and the temperature of gasification reaction zone should be controlled away from 700 ℃ ,which is beneficial to the formation of H2 and CH4, so as to improve the efficiencyand clean development of underground coal gasification process. The research results can provide guidance for the underground coal gasification process of lignite in Xishanyao Formation of the Santanghu Basin.