Aimed at the special environment of high pressure in deep sea, the existing structure of O-ring were optimized and improved to make it have better sealing performance under deep sea. The two-dimensional(2-D) model of O-ring was created by using the ANSYS software. Some factors influencing the sealing performance of O-ring under deep sea environment were analyzed, such as the diameter and depth of seal groove, the material of O-ring and the flange clearance. The results indicate that the diameter of the seal groove should be increased properly to avoid the formation of cavities between the compressed O-ring and groove wall when it is compressed under the deep-sea environment. The O-ring with NBR as the sealing material, which compression ratio is from 20% to 25% and clearance of sealing is zero, is suitable for using at the special environment of high pressure in deep sea.