The utility model provides a device for replacing a tension insulator string on a high voltage line. The device is characterized in that a large knife rest pulley is changed, a rope is pulled by a ground worker under a line tower, and an insulator string is pulled to be horizontal, so that the working strength of works on the tower is reduced, and the operation safety is improved. The adopted technical scheme is that the device for replacing the tension insulator string on the high voltage line comprises a fixing plate, a connection rod, a large knife rest, a carriage and a stay rope. The fixing plate and the large knife rest are fixedly connected through the connection rod. One end of the carriage is hinged to the fixing plate, and the other end of the carriage is connected with the stay rope. One end of the stay rope is tied to the carriage, and the other end of the stay rope passes through the large knife rest and extends to the ground. The large knife rest is configured to comprise a large knife rest body and a pulley assembly which is universally connected on the large knife rest body. The device for replacing the tension insulator string on the high voltage line can be widely applied to the field of electric power maintenance.