The H-mode initiated by the control of the rotational transform profile in CHS exhibits a very rapid transition (in 100 s or less) in NBI heated plasmas. There is no obvious difference in transition behaviour between hydrogen and deuterium. Langmuir probe measurement has revealed that the rapid change in floating potential occurs at the transition, but the change follows the formation of an edge transport barrier. The presence of an surface just inside the last closed flux surface and a sawtooth crash triggered by internal modes play an important role in the H-mode transition of CHS.