Offshore oil exploration in deeper waters has necessitated the development of lighter mooring systems to replace traditional steel cable and chain platforms. This study focuses on evaluating the mechanical behavior and fatigue degradation mechanism of high modulus polyethylene (HMPE) fibers in yarn-on-yarn abrasion tests. Initial characterization tests, including linear density, rupture force, and thermal analysis, were conducted on HMPE yarns. Yarn-on-yarn abrasion tests were performed under dry, wet, and salty conditions, with varying loads, while statistical analysis examined the influence of environmental factors and load levels on yarn performance. Scanning electron microscopy (SEM) analysis provided insights into material degradation mechanisms. Results showed superior performance in freshwater-immersed yarns due to cooling and lubrication effects, while dry conditions led to material melting. SEM analysis revealed critical degradation zones, particularly in interwoven regions, where increased friction and heat concentration caused material fusion. Degradation evolution mechanisms highlighted fatigue-induced rupture of yarns, knot formation, and material melting near failure points. This comprehensive analysis enhances understanding of HMPE yarn performance and degradation in offshore mooring applications, laying the groundwork for developing advanced mooring systems capable of withstanding deep-sea environments.