Efficient cooling of high-temperature synthesis gas produced in underground coal gasification systems is essential for improving process efficiency and ensuring operational safety. Conventional heat exchanger designs often face limitations in heat transfer performance when subjected to high-pressure and high-temperature gas flows. Recent advancements in additive manufacturing enable the fabrication of complex internal geometries that can significantly enhance heat transfer performance while maintaining compact system dimensions.The present study proposes a topology-optimized compact helical heat exchanger for high-pressure syngas cooling applications. A computational framework combining topology optimization and computational fluid dynamics (CFD) simulations was developed to identify optimal internal flow structures that maximize heat transfer while minimizing pressure losses. The optimized geometry was further evaluated under realistic operating conditions corresponding to underground coal gasification environments. The numerical simulations were performed using ANSYS Fluent to analyze turbulent compressible flow of syngas within the heat exchanger. The influence of optimized internal structures on temperature distribution, flow mixing, and pressure drop characteristics was investigated. The results indicate that the topology optimized design significantly enhances convective heat transfer by promoting secondary flow structures and improved fluid mixing. Compared with conventional helical coil heat exchangers, the optimized design achieved an increase of approximately 35% in heat transfer performance while maintaining acceptable pressure drop characteristics. Furthermore, the compact structure enabled a reduction in heat exchanger volume by nearly 20%, making it suitable for integration into high-temperature energy systems. The study demonstrates that the combination of topology optimization and additive manufacturing provides a promising approach for developing next-generation heat exchangers for underground coal gasification and other high-temperature industrial applications.