煤炭地下气化是保障我国能源安全和煤炭清洁利用的重要潜在方向之一。分析国内外相关成果，对煤炭地下气化原理、影响因素及评价方法进行述评。适宜于地下气化的煤层需要满足的地质条件：厚度大于2 m，倾角小于70°，阻水隔热的顶底板；避开地质构造和水文地质条件复杂的区域。地下气化煤气组分受煤阶、煤质和煤层含水性等地质因素以及气化压力、温度和气化剂类型等工艺因素共同影响。空气气化条件下，随着煤化程度增强，煤气组分中CO含量升高，H2含量降低，CH4含量先升高后降低。煤气热值及煤气中CH4含量随着固定碳含量增加呈现先降低后升高的趋势，随着灰分产率增加呈现先升高后降低的趋势。煤气中CO2含量与固定碳含量、灰分产率均表现出负相关关系。气化温度和气化剂类型既影响着产气效率、煤气质量及污染物种类与含量，又可使围岩破裂、污染地下水，乃至破坏生物圈、大气圈、水圈和岩石圈生态系统的稳定。

Underground coal gasification（UCG） is one of the important potential directions to ensure my country's energy security and clean coal utilization. Analyze relevant domestic and foreign results,and review the principles,influencing factors and evaluation methods of UCG. The coal seam suitable for underground gasification needs to meet the geological conditions:the thickness is greater than 2 m,the inclination angle is less than 70°,the roof and floor with water blocking and heat insulation;avoiding areas with complex geological structures and hydrogeological conditions. The composition of UCG is affected by geological factors such as coal grade,coal quality and water content of coal seams,as well as process factors such as gasification pressure,temperature and gasification agent type. Under air gasification conditions,as the degree of coalification increases,the CO concentration in the gas component increases,the H2 concentration decreases,and the CH4 concentration first increases and then decreases. The calorific value of coal gas and the content of CH4 in coal gas show a trend of first decreasing and then increasing with the increase of fixed carbon content,and a trend of first increasing and then decreasing with the increase of ash yield. The CO2 content in coal gas has a negative correlation with fixed carbon content and ash yield. The gasification temperature and the type of gasification agent not only affect the gas production efficiency,gas quality,and the type and content of pollutants,but also can rupture surrounding rocks,pollute groundwater,and even destroy the stability of the biosphere,atmosphere,hydrosphere,and lithosphere ecosystem.