A torque system of a power tool includes a combination of a first body and a second body, in which a toothed ring is assembled; and a mode selecting assembly, a torque adjusting module and control pins disposed on the second body. The torque system further includes restricting mechanisms formed on the second body, and the control pins are respectively disposed in the restricting mechanisms. One side of the control pin has a stopper block, and the restricting mechanism includes a first stopper, a second stopper and a through hole. When the control pin is driven to rotate and the stopper block faces the first stopper or the through hole, the object of switching each operation mode is achieved.