In the process of tension release of EHV transmission lines, the breaking of the traction line will lead to serious accident of whipping of both the wire and the moving plate, and cause great loss to the important facilities in the transmission line. In order to prevent similar accidents from happening, by analyzing the motion characteristics of the line upon breaking, an anti-slip-line device is designed, which can lock the traction rope immediately after it’s broken. Through calculation analysis and practical engineering application, the device can meet the needs of field engineering application. Multiple tests of the anti-slip-line device show that the average slip-away distance of the traction rope is 0.89 m, and the average reaction time of the device is 0.426 s, which means that the device can effectively avoid accidents and can be used as an effective measure to prevent accidents by traction rope breaking.