To promote equity and expand the spatial and social reach of multimodal rail systems, this paper examines the intersection of multimodal transit and social equity. It analyzes key research approaches, critical challenges, and influencing factors, and proposes future research directions and policy strategies. Findings suggest that two fundamental issues underpin the inequity of multimodal rail systems, namely spatial disparities in network coverage and insufficient attention to the diverse needs of users. Rail station and line densities tend to be lower in low-density urban neighborhoods and peri-urban or rural areas, making access more difficult. Vulnerable groups, including the elderly, people with disabilities, low-income populations, and individuals with lower educational attainment, are particularly affected by economic constraints, digital exclusion, and time-space coordination challenges in their daily mobility. Future research on social equity in multimodal transit systems should adopt a holistic perspective that integrates built environment characteristics, transport infrastructure provision, temporal factors, individual attributes, economic policies, intermodal connectivity, and digital literacy. Advancing equity in this context requires innovation in methodological frameworks, model development, as well as the identification and quantification of influencing mechanisms. As a capital-intensive foundational infrastructure, urban rail transit plays a critical role in shaping inclusive and equitable transport systems. Addressing social equity in multimodal transit is vital for enhancing population mobility, increasing employment opportunities, and promoting balanced and sustainable regional development.