The influence of hydrogen on microstructure evolution, metastable phase transformation and deformation behaviors of Ti–6Al–4V alloys were studied. Optical microscopy (OM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were utilized to study the phase composition and Ti–6Al–4V–H metastable phase transformation. Uniaxial compression test, tensile test and impact test were conducted to investigate the effect of hydrogen on the room temperature plasticity. A completely martensites microstructure, composed of α′ and α′′ martensites, was obtained in specimen with less than 0.45wt.% H. And the amount of α′′ increased with the increase of hydrogen concentration. Further increase in hydrogen concentration (above 0.45wt.%) resulted in a decrease of the volume fraction of α′′ and the formation of β phase. As a result, the deformation limit increased in compression test. However, the elongation decreased dramatically in tensile test. Compact test identified the decrease of plasticity was induced by hydrogen alloying.