The invention discloses a robot self-borrowing force wrench device. A planetary gear group structure is adopted, so that a wrench and a wrench supporting frame rotate reversely, torque is provided forscrewing down or loosening a bolt by using the interaction between the wrench supporting frame and a hardware fitting of a fixed bolt, and the weight of a robot body and the mechanical strength of amechanical arm are not depended on. The technical problems that the weight of the robot is heavy, the practicability is limited and the site operating efficiency is affected due to the fact that an existing wrench used for fastening the hardware fitting need to depend on the weight of the robot body to operate are solved.