The annular plane metal seal is an important sealing part of the gate valve of the gas tree,and its sealing performance directly affects the gas recovery efficiency.In order to develop the annular planar metal seal used in ultra-high pressure environment,stainless steel 718 was selected as the sealing material,and the relationship between the minimum contact stress and pressure was obtained through the test.The minimum contact stress was substituted into the valve-gate finite element model of metal seal,and the influence of seat face diameter and metal seal face width on sealing performance was analyzed,as well as the contact stress distribution at different temperatures.The simulation results show that the larger the inner valve face diameter is,the higher the reliability of metal seal is.Sealing surface width has no obvious effect on sealing performance.The ultra-high pressure test results show that the annular planar metal seal can still maintain good sealing performance under 140 MPa pressure,which verifies the reliability of the metal seal under ultra-high pressure.