The utility model relates to a screw thread installation formula high pressure fusion tube compares with prior art and to have solved the fusion tube structural design defect that fusible core changed of not being convenient for. The utility model discloses a tube cap is installed to fusion tube overcoat, the upper end of fusion tube overcoat, and the tube cap is installed down to the lower extreme of fusion tube overcoat, last tube cap be the internal thread structure, the upper end of fusion tube overcoat is the external screw thread structure, the upper portion of going up the tube cap is equipped with the boss, the wired nose connecting block of installation on the boss, the lateral part of going up the tube cap is equipped with the through -hole, the lateral part of fusion tube overcoat upper end is equipped with the notch, the through -hole be the internal thread structure, go up the tube cap screw and install in the upper end of fusion tube overcoat and act as tube cap and the installation of fusion tube overcoat to put rear through -hole in place corresponding with the position of notch, the threaded screw install on the through -hole and the threaded to on the notch. The utility model discloses the mounting means of fusion tube has been simplified.