The deformation mechanisms in the alpha-Fe twist bi-crystals (TBCs) containing differently angled twist grain boundaries (TGBs) are investigated carefully using the molecular dynamics modeling, with especial concerns on how solute hydrogen affects them. The results show that there are three main deformations in the TBCs, i.e. the dislocation glide dominated mechanism, the twining-dominated mechanism, the dislocation glide and twining co-dominated mechanism, depending upon both the twist angle and the loading direction. In the dislocation glide-dominated TBCs, solute hydrogen increases the dislocation nucleation strength, dislocation mobility and dislocation density, further increases the vacancies concentration due to frequent interactions of solute hydrogen atoms with dislocations. In the dislocation glide and twining co-dominated TBCs, the solute hydrogen has weaker effect on the increase of dislocations density and the decrease of twins fraction with increasing tensile strain. However, in the twining-dominated TBCs, solute hydrogen assists the deformation twinning but doesn't increase significantly the vacancies concentration. So, it seems that twinning deformation is beneficial to resist hydrogen embrittlement (HE). These knowledge is helpful for us to understand the HE mechanism and develop new hydrogen-resistant high-strength materials. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.