Large-scale and highly oriented single-crystalline hexagonal Cu2O nanotube arrays have been successfully synthesized using a two-step solution approach, which involves the electrodeposition of oriented Cu2O nanorods and a subsequent dissolution technique along the c axis to form a tubular structure. Herein, NH4Cl was found to be an effectual additive, and it can successfully realize the dissolution process of Cu2O from nanorods to nanotubes. The dissolution mechanism of Cu2O from nanorods to nanotubes was illustrated in detail. These prepared Cu2O nanotube arrays were characterized by SEM, EDS, XRD, XPS, and TEM. The photoluminescence (PL) spectrum of Cu2O nanotube arrays was also measured, and it shows there is a greater fraction of copper or oxygen vacancies in these prepared Cu2O nanotubes. Finally, the applications of Cu2O nanotube arrays for gas sensors were investigated in this paper.