A powered backpack device for assisting a human to walk with a load comprising a base plate and a load, a ball screw an elastic rope, a data acquisition module, a motion control module, a power supply and a controller arranged on the base plate, wherein the ball screw is arranged in the center of the base plate; the load is arranged on the ball screw and is driven by the motion control module to move up and down on the ball screw; one end of the elastic rope is fixedly arranged on the base plate, and the other end of the elastic rope is connected to the load by pulleys; the gravity of the load in a vertical direction is balanced by virtue of the traction of the elastic rope on the load; and the power supply is connected to the data acquisition module and the motion control module to respectively supply power to the data acquisition module and the motion control module; the data acquisition module and the motion control module are simultaneously connected to the controller; when the human starts walking with the backpack device on the back, the device enters a working mode under which the data acquisition module acquires a vertical acceleration of the human trunk in motion and transmits the acquired acceleration to the controller, and the controller sets a desired vertical acceleration of the load according to the vertical acceleration of the human trunk and makes the motion control module to drive the load to move at the desired acceleration on the ball screw; and when the human stops walking, the device enters an idle mode under which the data acquisition module acquires the position of the load and transmits the position of the load to the controller, and the controller makes the load stay on the ball screw by virtue of the motion control module. the ball screw is arranged in the center of the base plate; the load is arranged on the ball screw and is driven by the motion control module to move up and down on the ball screw; one end of the elastic rope is fixedly arranged on the base plate, and the other end of the elastic rope is connected to the load by pulleys; the gravity of the load in a vertical direction is balanced by virtue of the traction of the elastic rope on the load; and the power supply is connected to the data acquisition module and the motion control module to respectively supply power to the data acquisition module and the motion control module; the data acquisition module and the motion control module are simultaneously connected to the controller; when the human starts walking with the backpack device on the back, the device enters a working mode under which the data acquisition module acquires a vertical acceleration of the human trunk in motion and transmits the acquired acceleration to the controller, and the controller sets a desired vertical acceleration of the load according to the vertical acceleration of the human trunk and makes the motion control module to drive the load to move at the desired acceleration on the ball screw; and when the human stops walking, the device enters an idle mode under which the data acquisition module acquires the position of the load and transmits the position of the load to the controller, and the controller makes the load stay on the ball screw by virtue of the motion control module.