Abstract: Applying the theory of nonlinear finite element analysis, the stresses and strain of the elastomeric O-ring seals at storage and working process were analyzed. The factors influencing sealing performance were considered, such as gap between upper and nether flange, initial compressibility, groove width, sealing materials, O-ring section diameter and the work temperature. Results show that the gap breadth, initial compressibility and seals material do great contributions to the maximum contact normal stress, and the groove notch and bottom fillets act upon the maximum shear stress obviously. The analysis lays the foundation of the optimum design of sealing structure. Based on the stresses distribution and the brittle position, the failure mode & criteria were discussed and established.