A butt joint method of HTc superconductor has been investigated for a concept of remountable superconducting (SC) magnets in fusion reactors. Through numerical analysis of the present study, it is clarified that the degradation of SC tape near the surface had influences on the joint performance. This degradation of SC tape gives the relationship that the resistance in the butt joint increases when the transport current increases in the butt joint. And through the experiment, the optimum stress, which gives the minimum resistance at the joint, is determined for the butt joint of SC cable composed of ten of SC tapes. The joint resistance of a butt cable shows a larger value than predicted from the experiment using a single layer SC tape.