Basic fundamentals governing the hydrogenation of Zr and its alloys have both theoretical and practical importance.In this work,first-principles calculations have been performed to evaluate the relative stabilities of various possible phases in ZrHx (x =1-2) under different temperatures and pressures.It was predicted that fct-γ and e phases with various different H-atom configurations can be energetically favorable for ZrHx (x=1,1.25 and 1.5),while ZrH1.75 and ZrH2 prefer fct-e phase only.Fcc-δ phase is less favored in energy at any H concentrations,but can be mechanically stable in some cases.The thermodynamically stable and metastable phase stability diagrams were then constructed for a wide temperature and H concentration range,to predict the environment-dependent formation of ZrHx during hydrogenation.