The invention discloses a locking device of an extrusion machine for manufacturing a power line. The locking device comprises a frame which has a through structure. The upper end and the lower end ofthe left inner wall of the frame are respectively provided with a rotating seat which is fixedly mounted. A first bolt is inserted into the rotating seat. The right end of each first bolt penetrates through the frame. The left end and the right end of the surface of the first bolt in the frame are respectively provided with a left thread and a right thread. The top end and the bottom end of a leftlock clam and a right lock clamp are respectively provided with two through holes. Second bolts are inserted into the through holes. The bottom end of each second bolt is connected with a first clamping plate. The leftmost end of the inside surface of the left lock clamp and the rightmost end of the inside surface of the right lock clamp are fixedly connected with a second clamping plate. Furthermore the second clamping plate and the first clamping plate respectively abut against the left lock clamp and the right lock clamp closely. The locking device can clamp the core wire of the power linein an upper direction, a lower direction, a left direction and a right direction, so that better locking capability of the device is realized. Furthermore the locking device is provided with a buffering protecting device, thereby preventing deformation of the core wire of the power line because of squeezing and realizing high popularization value.