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Inspired by recent progress of experimental fabrication of partial structure of the helical graphenes, we construct helical graphene nanoribbons and study the electronic structure and transport properties of them, through first-principles calculations. It is found that a metal-semiconductor transition occurs when the pitch of the configuration changes, and the whole transition process can be divided into three regimes, ie, metallic, fast changing bandgap, and slowly changing bandgap ones. Further analysis shows that, interlayer transmission, interlayer interaction (bilayer graphenelike state) and intralayer interaction are the mechanisms behind, respectively. Moreover, such a transition and corresponding mechanisms show good robustness to the size of the helical graphene nanoribbons, suggesting great application potential. As the systems are pure-carbon and graphene-based ones, as well as an adjustable and …