To investigate the changes of organic and inorganic substances produced by coal heat pyrolysis in the dry distillation channel in coal underground gasification, lignite coal was used as the object of this study. The pyrolysis reaction in the range of room temperature to 600 degrees C was carried out using coal pyrolysis reactor of high-temperature tubular heating furnace. SEM, FTIR and x-ray diffractometer analyzed the sample. The results show: The increase in pyrolysis temperature leads to a decrease in tar yield and an increase in gas and char coke yield. The surface of the coal sample shows molten state and gradually harden. The expansion of porosity accelerates the transportation of gas in coal seams. Coal pyrolysis is prone to hydrogen bond breakage at 400 degrees C. In addition, the content of unsaturated halogenated hydrocarbons increases under pyrolysis. (C) 2020 Elsevier B.V. All rights reserved.