The invention discloses an energy absorption device and method for a child safety seat restraint strap. The device comprises an energy absorption barrel, hook pieces, springs, a piston, honeycomb aluminum and a piston rod; the top of the energy absorption barrel is sealed, and an opening is formed in the bottom of the absorption barrel; the springs, the piston and the honeycomb aluminum are located in the energy absorption barrel; the tops of the springs are fixedly connected with the top in the energy absorption barrel, and the bottoms of the springs are fixedly connected with the top surface of the piston; a cavity between the bottom surface of the piston and the bottom of the energy absorption barrel is filled with the honeycomb aluminum; the top of the piston rod is fixedly connected with the bottom surface of the piston, and the bottom of the piston rod penetrates out of the opening in the bottom of the energy absorption barrel; the bottom of the piston rod is fixedly connected with a hollow block, and the hook pieces are arranged on the top of the outer side of the energy absorption barrel. When collisions occur, the forward movement of a child drives the shoulder belt restraint strap to move forward, and collision impact borne by the child is greatly reduced due to friction among the honeycomb aluminum, the piston and the wall of the energy absorption barrel. The energy absorption device is simple in structure, remarkable in energy absorption effect and convenient to manufacture.