Abstract: The O-ring sealing structure of deep-sea beacon used in oil drilling platform is taken as the research object, O-ring and its boundary conditions model is created by using finite element analysis (FEA) software ANSYS, the stress distribution of the sealing surface and Von Mises stress distribution caused by O-ring deformation are calculated under the conditions of different rubber compression ratio and working depth. Analysis shows that：increasing the O-ring compression ratio could increase the sealing surface contact stress and improve the sealing performance, however, excessive compression ratio would cause the stress relaxation of the rubber material, resulting in seal failure. As working depth increases, the sealing performance of structure would decrease. In this paper, a method of designing suitable compression ratio of O-ring by using FEA software is put forward, which can ensure that the sealing structure has good sealing performance. And the method has been successfully applied to domestic beaconof oil drilling platform, but also can provide a reference and guidance for deep-sea O-ring selection and structure design.