Abstract: Repair clamp is a key fixture for emergency maintenance of subsea pipelines. In this paper, it was determinedby analyzing the working principle of the repair clamp that the key factor to the design of repair clamp is the size designof sealing structure. The load-deformation curve of the axial graphite sealing strip was measured by means of compressionrebound test. According to the calculation result, the engineering stress of the sealing strip reaches 3 MPa when theengineering strain of the graphite sealing strip reaches 0.18, or the engineering strain of the fluorine rubber sealing stripreaches 0.25. Then, the average contact pressure of the semi-sealing ring at different compression ratios was analyzed. It isshown that the average contact pressure of graphite semi-sealing ring and that of fluorine rubber semi-sealing ring are bothabove 4 MPa when their radial compression ratio reaches 12.5%. After the size of the sealing structure was determined, the application advantages and disadvantages of graphite and fluorine rubber to the sealing of repair clamp were comparedthrough hydraulic pressure test. It is indicated that graphite can be used as the sealing material of repair clamp, and itperforms well when the pressure is lower than 2 MPa. Under the same bolt load, the sealing performance of fluorine rubberis better than that of graphite. In addition, the sealing of graphite material will not get failed due to aging, so graphite-basedsubsea pipeline repair clamp is promising in application prospects.