AbstractThe thermal stability of the superconductor KISO-3B, which has been one of conductors developed for LHD coil, is analyzed numerically on a two-dimensional model. The computational results show that the threshold of thermal disturbance from a recovery to a quench is clear and the change from a recovery to a quench is produced by a slight difference of several percent in the magnitude of thermal disturbance. In the case of a recovery the superconductor state area spreads over the whole conductor instantaneously after it appears locally in the cross section of the conductor by the decrease in temperature according to the relation between the rates of Joule heat generation and heat transfer.