Abstract： Subsea permafrost, formed by the inundation of terrestrial permafrost due to the sea-level variations during the glacial-interglacial cycles, is mainly distributed across the Arctic continental shelf. However, there is a large uncertainty in its distribution extent (approximately 1~2.7 million square kilometers). Subsea permafrost is considered a significant carbon reservoir in the Earth system, which stores vast amounts of organic carbon (OC) and methane (CH₄) gas. With global warming and rising temperatures of Arctic Ocean waters, subsea permafrost is undergoing rapid degradation, which may exacerbate carbon release risks. Consequently, the subsea permafrost plays a significant role in influencing the global carbon cycle and climate change. The large CH4 emissions into the atmosphere have been observed in the East Siberian subsea permafrost region. However, the rates of subsea permafrost degradation, the magnitude of carbon reservoirs and gas release are still not clear. In particular, due to the rapid Arctic warming, the northward expansion and intensification of the North Atlantic Current which exacerbates the Atlantification of the Arctic Ocean, and dramatic increases in human disturbance, the climate risk would increase by the accelerated emission of CH4 from Arctic subsea permafrost. These variations will influence the human sustainability in the future. This paper systematically summarizes the spatial distribution, degradation rates, and carbon storage in Arctic subsea permafrost. The applications of methods for CH₄ monitoring in the subsea permafrost were reviewed, including the fixed-point observations, aerial surveys, and remote sensing. Furthermore, this paper discusses factors influencing CH₄ emissions, highlights the importance of studying the characteristics of Arctic subsea permafrost and its carbon cycle for global climate change, and identifies current challenges and suggests future research directions.