Abstract: The numerical model of O-ring used in compensatory configuration of mechanical seal was established by finite element method. Von Mises stress and Contact stress of O-ring were obtained using a nonlinear finite element software-MSC.MARC. Experimental results of frictional force were gained on a high frequency fatigue machine and a water lubricated O-ring tester. The effects of amount of compression and operation parameters on contact stress and frictional force were analyzed. The effects of the O-ring used in compensatory configuration of mechanical seal on sealing performance, such as sealing capability, characteristic of leakage, were discussed. The results indicated that the use of O-ring in compensatory configuration of mechanical seal can lead to micro leakage, and water film can be developed between contacting surfaces under water lubrication, which led to reduction of frictional force and stability of performance.