The utility model relates to a drainage bolt of the last use of transmission line specifically is 500kV transmission line strain insulator tower drainage check bolt. 500kV transmission line strain insulator tower drainage check bolt, including the bolt body, supporting on the bolt body have card dental pad piece, and the pitch of bolt body is 1.5mm, and thread angle is 60, blocks the dental pad piece and is formed by last gasket and lower gasket laminating, and upward the lateral surface of gasket and lower gasket is radial burr face, and the subsides of going up gasket and lower gasket are the skewed tooth face at the back, and the skewed tooth face slope is greater than the thread angle of bolt body. The utility model discloses a gasket outside have the design of radial burr, it has goodfrictional property between bolt and the gasket to make, the latch skewed tooth face slope is greater than thread angle makes the bolt have good auto -lock performance. The labor intensity of the fastening rate once more of strain insulator tower drainage bolt to a present operator member is reduced with the reduction interruption maintenance time.