The working principle of hydraulic power tong is to transfer the power of the workover rig to the hydraulic motor of the hydraulic power tong, which passes through a stroke reducer, and then undergoes two or one stage reduction, causing the opening gear of the tong head to rotate, generating high and low speeds, thereby driving the rotation of the pipe (drilling tool). When the open gear rotates, the plate frame does not rotate under the braking effect of the brake hammer, causing a relative motion between the open gear and the palatal plate frame. In this way, the two rollers of the palatal plate will climb the slope on the slope and force the pliers on the hip plate to move towards the center of the pipe (drilling tool) until they bite tightly, and then work together with the open gear to drive the pipe (drilling tool) to rotate.