The subgrade is an essential structural foundation in high-speed railway engineering, and its long-term stability directly affects railway transportation safety. With continuously increasing train speeds and axle loads, cumulative settlement of subgrades under dynamic loading is becoming increasingly prominent. Consequently, it has emerged as a critical interdisciplinary research hotspot across railway engineering, geotechnical engineering, and engineering mechanics. This paper reviews domestic and international research achievements regarding cumulative settlement of subgrades subjected to high-speed train loading. Specifically, it summarizes recent developments in experimental investigations, theoretical analyses, and influencing factors related to cumulative settlement, highlighting the complexity and key technical challenges associated with long-term subgrade deformation. Moreover, the paper outlines future research directions, including examining the effects of intermittent loading on long-term deformation, as well as investigating the particle breakage mechanism of subgrade fill materials and its impact on deformation behavior. This review aims to provide theoretical support for the design and optimization of high-speed railway infrastructures.