The utility model discloses a but open -close type track tensioning device, including the base, set up braced frame, the bilateral symmetry on the base and can open and shut relatively to set up two first track systems and the longitudinal symmetry on braced frame and can open and shut relatively and set up two second track systems on braced frame, the braced frame middle part is equipped with the first passageway and the second channel of looks vertical cross and intercommunication, and the crossing position of first passageway and second channel forms the centre gripping passageway, two first track systems are arranged in first passageway in centre gripping passageway relative both sides, and two second track systems are arranged in the second channel in centre gripping passageway in addition relative both sides, and first track system and second track system open and shut with the centre gripping pipeline respectively relatively. The utility model discloses in, the centre gripping can be carried out to the pipeline through among them to symmetry through four track systems, the setting of can opening and shutting relatively, because centre gripping in the time of through four track systems for it is more even by centre gripping pipeline atress, be difficult for causing the pipeline to warp.