According to the characteristics of marine oil and gas,the main sealing devices used in the subsea wellhead system were summarized,current situation procession of the development of sealing technology and device of subsea well system were introduced.The difference between subsea well system seal and conventional seal was analyzed,the key technology of sealing used in subsea well system was summarized.It is concluded that the main trend of subsea well system sealing depended on the marine oil and gas development in the future is metal sealing，and is pointed out that the formulation of relevant industry standards will promote the development of underwater sealing technology.