The utility model relates to a tightening device, particularly to an insulated tightening device. A protruding edge (2) is arranged at the upper portion surface of the outer edge of a tightening box (9); at least two connecting columns (6) are arranged in a cavity (8) at intervals, wherein the cavity (8) is formed at the upper portion surface of the tightening box (9) in the protruding edge (2); and screw holes (5) are formed in the upper ends of the connecting columns (6). Openings (7) are respectively formed in the two sides of the protruding edge (2). Holes (4) corresponding to the connecting columns (6) are formed in a cover (3); screws (10) pass through the holes (4) in the cover (3) and then are connected with the screw holes (5) of the connecting columns (6). According to the technical scheme, the electric wire is tightened by using the connecting columns or winding posts of the tightening box, thereby preventing the electric wire from being worn due to the influence of the wind power.