The invention discloses a J-type wire clamp live-wire-connecting device and system in a live working state and a J-type wire clamp clamping mechanism. The J-type wire clamp live-wire-connecting devicein a live working state comprises a base, a striking device, a left wire clamp frame, a right wire clamp frame, and a wire clamp clamping mechanism. The wire clamp clamping mechanism is used for clamping a horizontally placed J-type wire clamp, and comprises a front stop assembly, a sliding seat movable forward and backward relative to the front stop assembly, a first elastic element and a rear stop assembly. The fastening sleeve for power output of the striking device is configured to be engaged with the head of a bolt of the J-type wire clamp in order to screw the bolt. The fastening of theJ-type wire clamp is completed by the striking device, which achieves high efficiency, high labor efficiency, large fastening torque and reliable fastening. Through the specially designed wire clampclamping mechanism, the J-type wire clamp is clamped in a horizontal state such that the problem is solved that a J component has a complicated shape and is difficult to position and clamp.