The invention relates to an axial force balancing device for a single-stage radial turbo-expander and a design method. The axial force balancing device comprises a thrust bearing, a back cavity comb tooth sealing ring, a bearing lantern ring, a spindle, a thrust bearing comb tooth sealing ring and an impeller. The thrust bearing, the thrust bearing comb tooth sealing ring, the bearing lantern ringand the impeller are all mounted on the spindle, and the back cavity comb tooth sealing ring is mounted on the bearing lantern ring. One end of the thrust bearing makes contact with one end of the thrust bearing comb tooth sealing ring, the other end of the thrust bearing comb tooth sealing ring makes contact with one end of the bearing lantern ring, the other end of the bearing lantern ring makes contact with the impeller, and the impeller is mounted at the end of the spindle. (1), axial force generated by the radial turbo impeller can be effectively reduced; (2), the bearing lantern ring issimple in structure and easy to machine; (3), the problem about axial force can be relieved under the condition that existing equipment is slightly modified; and (4), the equipment can be simplifiedand miniaturized.