Subsea permafrost, formed by the inundation of terrestrial permafrost due to sea-level variations during the interglacial cycles, is primarily distributed across the Arctic continental shelves. However, a substantial uncertainty remains regarding the extent of its distribution (approximately 1~2.7 million square kilometers). Subsea permafrost is considered a significant carbon reservoir in the Earth’s system, storing vast amounts of Organic Carbon (OC) and methane (CH₄). With global warming and rising Arctic Ocean temperatures, subsea permafrost is undergoing rapid degradation, potentially exacerbating carbon release risks. Consequently, it plays a significant role in the global carbon cycle and climate dynamics. Large-scale CH₄ emissions into the atmosphere have been observed in the East Siberian subsea permafrost region. However, the rates of subsea permafrost degradation, the size of carbon reservoirs, and gas release remain poorly constrained. In particular, rapid Arctic warming, the northward expansion and intensification of the North Atlantic Current (which exacerbates the Atlantification of the Arctic Ocean), and increased human disturbances have intensified climate risks due to accelerated CH₄ emissions from Arctic subsea permafrost. These changes have significant implications for future human sustainability. This study systematically summarizes the spatial distribution, degradation rates, and carbon storage of Arctic subsea permafrost. It also examines CH₄ monitoring in subsea permafrost, including fixed-point observations, aerial surveys, and remote sensing technologies. Furthermore, it discusses the factors influencing CH₄ emissions, emphasizes the importance of understanding Arctic subsea permafrost dynamics within the context of global climate change, identifies key challenges, and suggests future research directions.