Abstract: In this paper, the axisymmetric computational model of rubber O ring in mechanical seal is established with the finite element analysis software ANSYS. The deformation, Von Mises stress distribution, contact pressure and friction with sleeve in two different mounting states are calculated, and the influences of medium pressure, groove width and compression ratio on the performance of O ring are also obtained. The results show that the deformation, Von Mises, contact pressure and friction with sleeve increase with the increasing of medium pressure and compression ratio, while decrease with the increasing of groove width. Groove width can not be too narrow, and the compression ratio of O ring should be different in the different installation methods.