Abstract: Underground coal gasification represents a promising direction for the clean and efficient utilization of coal in the future and is expected to serve as a significant supplement to deep coal mining and utilization in China. However, the potential risk of groundwater contamination posed by organic pollutants carried by high-temperature syngas generated during UCG has emerged as a bottleneck constraining the industrial application of this technology. Addressing the unclear mechanism of coal tar formation under the high-temperature and high-pressure conditions in the drying and pyrolysis zone during deep UCG, this study employs a pressurized coal pyrolysis experimental apparatus combined with gas chromatography-mass spectrometry (GC-MS) to elucidate the distribution characteristics of pyrolysis products and the evolutionary patterns of tar chemical components, revealing the multi-stage formation mechanism of coal tar during deep UCG. The results indicate that under a pressure of 3 MPa, as the pyrolysis temperature increases, the char yield continuously decreases, while the yields of tar and syngas significantly increase. Specifically, at 500 °C, the syngas yield is 4.3 times higher than that at 400 °C, identifying this range as a critical temperature interval for enhancing gas production efficiency. The chemical composition of tar exhibits pronounced stage-wise transformation characteristics with increasing pyrolysis temperature. In the range of 400–500 °C, aliphatic hydrocarbons dominate the composition, accounting for 73.65% and 71.6%, respectively. At 600 °C, polycyclic aromatic hydrocarbons replace aliphatic hydrocarbons as the main component, with their proportion increasing from 1.25% and 4.21% at 400–500 °C to 48.67%. At 700 °C, non-hydrocarbon compounds become the core components of tar, accounting for 32.32%. Pyrolysis pressure significantly regulates the evolution of tar group components. Under atmospheric pressure pyrolysis conditions at 700 °C, the asphaltene content in coal tar peaks. As the pyrolysis pressure increases, the relative content of asphaltenes gradually decreases, while the relative content of saturated hydrocarbons gradually increases. When the pressure exceeds 2 MPa, saturated hydrocarbons are completely released, whereas the yields of aromatics, resins, and asphaltenes continue to increase with rising pressure. This study reveals the formation law of coal tar during pressurized pyrolysis, providing a theoretical basis for pollutant control and process optimization in deep UCG.