Abstract: In order to assure that the sealing structure can effectively prevent the leakage of the medium inside a tank, it is important that the sealing surface is under certain fasten pressure. Therefore, a proper tightening torque should be applied for the compression of the seal ring, to guarantee the sealing of the structure. At present, the critical value of the tightening torque is mainly obtained by carrying out a series of experiments with different torque values and testing the sealing effect, and a reliable design value of the tightening torque is then obtained subsequently. Based on the experience learned from those experiments, a reasonable hypothesis is made to establish a simplified nonlinear finite element model, which simulates the plastic deformation of the seal ring under a given pressure. The critical tightening torque value is then determined from the critical pressure, with the desired deformation to the seal ring. The design value from this simulation is in agreement with that from the experiments, and, therefore, this method can be used to improve the efficiency of the design and to reduce time and experimental costs.