Dusty tar is an undesired product obtained from a coal pyrolysis/combustion system. Thermal conversion of dusty tar into fuel gas was studied with a fixed-bed reactor. It is found that C-2-C-5 hydrocarbons are mainly derived from the cracking of long-chain aliphatics, while CH4 from the decomposition of long-chain aliphatics and alkyl-substituted aromatic chemicals. The yield of the gas product increases monotonously, but the heating value of gas gradually decreases as temperature increases from 400 to 950 degrees C. Decomposition of chemicals with aboiling point over 360 degrees C contributes to 50-90% C-1-C-5 hydrocarbons and COx when pyrolysis temperature is lower than 600 degrees C.