Annular metal seal assembly is an important part of the subsea wellhead system,its quality directly affects the security of subsea wellhead system,and even the reliability of subsea oil and gas system.By discussing the mechanism and working principle of annular metal seal assembly,the sealing performances were analyzed from the deformation of sealing ring in the sealing process and combining with the finite element analysis results.The results show that the seal can be achieved at the elastic deformation stage of sealing ring,but there is high demand of surface roughness and quality that the annular seal assembly cannot be guarantee under the working conditions.The sealing ring can achieve good seal because the surface defects of the sealing ring can be filled at the stage of plastic deformation.The deflection of the sealing ring contact surface becomes the only factor affecting sealing performance at plastic deformation stage.