Abstract: To investigate the issue of coal tar condensation and blockage during long−distance pipeline transportation in Underground Coal Gasification (UCG), this study was conducted within the context of a UCG project in Shandong, China. Condensed tar samples collected from a vertical borehole section (T1) and the purification area (T2) of the gas pipeline were analyzed using elemental analysis, Fourier Transform Infrared Spectroscopy (FTIR), and Gas Chromatography−Mass Spectrometry (GC−MS) to characterize their compositional features. The results indicate that T1 tar has a high carbon content of 90.80%, with hydrogen and oxygen contents of only 4.16% and 3.66%, respectively. Its composition is predominantly aromatic hydrocarbons (90.29%), among which polycyclic aromatic hydrocarbons (PAHs) constitute 84.94%. The molecular structure is characterized by highly substituted aromatic rings and oxygen−containing non−phenolic aromatic compounds. After pipeline transportation, the composition of T2 tar changes significantly. The carbon content decreases to 77.99%, representing a 14.11% reduction relative to T1. In contrast, the hydrogen and oxygen contents increase to 7.35% and 13.57%, marking relative increases of 76.68% and 270.76%, respectively. While the proportion of aromatic hydrocarbons rises slightly to 92.97% (a 3.08% relative increase), the proportion of PAHs within the aromatic fraction decreases to 79.79% (a 6.06% relative decrease). Furthermore, non−fused polycyclic aromatic hydrocarbons emerge as new components. The molecular structure shifts towards being dominated by mono−substituted aromatic rings with enriched oxygen−containing functional groups. This research provides a theoretical basis for understanding the formation and migration mechanisms of tar in UCG processes. It also offers scientific support for developing tar control technologies for pipelines and equipment in UCG engineering.