The utility model discloses a self -locking device, it sets up between emergency exit to the hand -operated direction valve in the hydraulic tong opening outside, include: the setting is in support on the emergency exit, mode setting through dismantling the connection is in first joint on the support, fix second on the hand -operated direction valve connects, in connecting, the second is provided with locking mechanical system, the power that passes, its have back to first end and second hold, first end with first joint fixed connection, the second is held and is worn to establish in the second connects with locking mechanical system cooperatees, when the emergency exit is opened behind the predetermined distance, the power that a passes change locking mechanical system's state makes the hand -operated direction valve is locked. The utility model provides a self -locking device can improve the barrier propterty of hydraulic tong linkage emergency exit, prevents that hydraulic tong hinders the emergence of hand accident.