With first-principles pseudo-potential plane-wave method, crystal structures, electronic structures and optical properties of sulvanite compounds:Cu₃VS₄, Cu₃NbS₄ and Cu₃TaS₄ are calculated to investigate their electrical conductivity and electrochromic performance. They are potentially applied in solar cells and electrochromic devices as transparent semiconductors. Electronic structures indicate that the secompounds are indirect band-gap semiconductors, with conduction band minimum and valence band maximum located at X and R points, respectively, in Brillouin zone. Electronic states of conduction band minimum and valence band maximum are dominated by d-orbitals of Cu and Ⅴ-group elements, respectively. From band structure, atomic charge population analysis, electron localization function and optical adsorption/reflectivity spectrum it is suggested that these sulvanite compounds are polar covalent semiconductors with high charge transport mobility and extraordinary electrochromic characteristics. They could be applied to electrochromic devices.