A full-metal dynamic-sealed concentrically-centered downhole displacement motor includes an outer tube, a stator fixed in the outer tube, a rotor rotatably connected in the stator, and a flow distribution shaft suspended in the rotor. When the rotor rotates, the plurality of circulation ports is alternately communicated with the flow distribution holes, and an accommodation space for flowing the drilling fluid is formed among the plurality of rotor copper rods; each of the circulation ports has a notch on the side of the rotor copper rod that is in communication with the accommodation space; the stator is provided with pressure relief ports for allowing the annular chamber and the accommodation space to communicate with each other, and the flow distribution hole and the pressure relief port are circumferentially arranged in a staggered manner.