The utility model provides a big two -way high -pressure combined seal ring in clearance, a serial communication port, include: annular guard ring, its peripheral surface are equipped with 2 at least annular grooves, at least 2 O shape sealing washer, every O shape sealing washer is located one in the annular groove. The utility model provides a big two -way high -pressure combined seal ring in clearance adopts at least two O shape sealing washer that is equipped with the annular guard ring of at least two rings connected in star and is located the annular groove, realizes the two -way pressurization in big clearance, and O shape sealing washer can be protected better in the design of annular groove.