Typically, the superconducting busbar of TOKAMAK feeder system is divided into different segments, which are connected by superconducting joints. ASIPP (Institute of Plasma Physics, Chinese Academy of Sciences) feeder team has improved the twin-box for ITER (International Thermonuclear Experimental Reactor) feeder systems. In the twin-box joint, the two cables were connected by two compressed against copper soles, and the pure indium was used as solder. For superconducting joint improvement, ASIPP feeder teams design a sub-cable overlap joint with smaller volume, lower resistance and more uniform tension insulators. In the sub-cable overlap joint, the cable is untwisted at the sub-cable stage, and sub-cables of two cables are connected by indium-coated copper soles. A brief analysis including resistance, AC losses and temperature rise produced by joints of the respective busbar with twin-box and sub-cable overlap joints was carried out in ITER 15 MA plasma current reference scenario. The sub-cable overlap joint has smaller resistance of 0.0776 n Omega and lower AC losses of 5.95 W than twin-box joint with 0.201 n Omega resistance and 1.182 W AC losses. The design length of sub-cable overlap joint is 300 mm, shorter than twin-box joint length of 450 mm. The cylindrical shape sub-cable overlap joint makes tension insulators much more uniform than that in twin-box joint.