In hexagonal close-packed titanium, the interactions between the (11 (2) over bar1) twin boundary (TB) and hydrogen solute atoms with several different concentrations are investigated by using first-principles calculations. The preferential occupation sites of hydrogen atoms in the (11 (2 ) over bar1) TB region are searched and vary with the amount of hydrogen. Both the shift of the TB and the diffusion of hydrogen atoms, as well as the mutual effect on the movement of each other, are studied. The energy barriers of the TB shift increase with the hydrogen concentration. Additionally, the simulated tensile tests are applied for several systems with co-existing (11 (2) over bar1) TB and hydrogen atoms, and different geometry transformation behaviors at different hydrogen concentrations are found under the increasing tensile strain. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.