We have calculated the electronic structure of ZnVSe2 by the method of first-principles plane wave pseudopotential (PWP) with density functional theory (DFT) combined with generalized gradient approximation (GGA), such as spin polarized energy band structure, density of states, Mulliken population, magnetic moments and so on. The calculation results show that ternary compound ZnVSe2 is a half-metallic ferromagnet that shows significant ferromagnetism, its half-metallic energy band gap reaches 0.443 eV. The electron spin polarization is as high as almost 100%, and therefore, ZnVSe2 may be a useful material for spintronics.