The hydrogen gas sensing properties of carbon-doped ZnO nanotube has been theoretically investigated by employing first-principles density functional theory in combination with non-equilibrium Green's function. The figure of merits is creating the new states in ZnO nanotube structure by adding carbon substitution for an oxygen site. The calculation of adsorption energy indicates strong chemical adsorption of hydrogen on the outside and inside of carbon-doped ZnO nanotube. Moreover, density of state, current-voltage and sensor response have been performed for energetically favorable adsorption geometries of hydrogen. The involvement of carbon valence electrons in the chemical adsorption of hydrogen has been examined by partial density of state diagram. The current-voltage diagram of carbon-doped ZnO nanotube indicates negative-differential resistance trend. This trend has been disappeared after the chemical adsorption of hydrogen. The sensor response calculations reveal the high response of the sensor occurs in 3.5 V on the outside and inside of carbon-doped ZnO nanotube. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.