Abstract: Using finite element computed program, O-ring seal performance by using flanges of stainless steel and aluminum alloy was analyzed. The elasto-plastic strain was considered in the finite element analysis. The calculated results show, for 5 mm×0.5 mm pre-tightened stainless steel O-ring, it has the best sealing capability when the compression ratio range is in the region of 10%-20%. The seal width is 0.2-0.3 mm, and the contact pressure is 80-120 MPa. The sealing pressure ratio is in the region of 100-130 N/mm, which agrees well with the design pressure force 120 N/mm.