Aiming at the problem of sealing failure of wellhead device in high temperature and ultrahigh pressure gas wells,the material selection and sealing mechanism of core shaft casing hanger are studied by using finite element method and indoor test method. Composite metal sealing ring material is put forward.The sealing surface is soft metal with high strength matrix.The sealing is achieved through plastic flow of soft metal and elastic deformation of matrix.The increase of the contact pressure of the linear sealing surface is smaller,while the sinusoidal and parabolic seals are increasing undulate,and the average contact pressure of the elliptical seal increases steadily, indicating that the elliptical contact surface is beneficial to the stability of the seal.The results of theoretical study and laboratory experiment show that the full metal multilevel conical elliptical surface sealing structure is reliable and can meet the sealing requirements of limit working condition under the 140 MPa of the oil field wellhead device.