Abstract: The structure characteristics of the CBFJ extreme-line premium connection are described.And the typical service conditions for the said connection are analyzed.Focused on are study of the connection efficiency and the sealing performance under the compound load conditions.Also described is the full-scale test result.The result reveals that the connection efficiency of the CBFJextreme-line premium connection is over 58%,while under complex loading,such as tensile,compression and both inside-outside pressures,though the contact stress of the connection is remarkably changed,but rather high sealing index is maintained,which means that the said connection can still maintain good sealing performance.