Abstract: Resources of low rank coal with high content of alkali and alkaline earth metals( AAEM) are rich in China. The serious problems,including slag-bonding,staining,erosion and agglomerating in boiler and gasifier,are caused due to high AAEM in coal. Meanwhile,low-rank coal is often characterized by particular features,such as high moisture content,high oxygen content,high volatile content,low caloric value and ease of spontaneous ignition,which bring great difficulties to its storage,transportation and utilization.Pyrolysis can produce high-quality fuel and high value-added chemical raw materials. Besides,pyrolysis can also be considered as the initial stage and/or paralleling part of coal combustion,gasification and liquefaction,and the reactions and behaviors in coal pyrolysis play an important and even decisive role in the thermal conversion of low rank coal. In the paper,a critical survey of investigation into coal pyrolysis and characterization of char derived from coal pyrolysis was presented,with emphasis on the influence of AAEM on coal pyrolysis. The results show that the apparatus and equipment used for pyrolysis study in labs and the set of experimental parameters are far from that in the process of modern coal chemical industry,and the representativeness of Semicoke sample is not strong enough to guide the research results of pyrolysis. The occurrence mode and separation method of AAEM in coal need to be improved and new extraction reagents need to be screened and tried. Although the behavior of AAEM in coal pyrolysis is basically grasped,there is not an effective method to reduce the harm of AAEM in coal thermal conversion process. Thus,safe,efficient and clean utilization of high AAEM low rank coal awaits researching and developing further.