The invention discloses a casing sealing ring. The casing sealing ring comprises a sealing ring, a jointing positioning sealing ring and a casing. The sealing ring and the jointing positioning sealingring are fixed to the end parts of two connected pipelines correspondingly, the casing sleeves the sealing ring and the jointing positioning sealing ring, a sealing structure is installed between thesealing ring and the jointing positioning sealing ring, the sealing structure is composed of a "C"-shaped annular sealing rubber ring and a supporting ring, the supporting ring is installed in the "C"-shaped annular sealing rubber ring, and one, two, or more through holes are formed in the supporting ring. According to the casing sealing pipe, the structure is simple and light, manufacturing is easy, assembling and disassembling are both convenient at various positions, and quick installation of the pipelines and the sealing quality of the pipelines at the high pressure or the low pressure can be ensured.