The　electronic　structures　and　optical　properties　of　II-III　2-VI4　(II　=　Zn,　Cd;　III　=　In;　VI　=　Se,　Te)　compounds　are　studied　by　the　density　functional　theory　(DFT)　using　the　Vienna　ab　initio　simulation　package　(VASP).　Geometrical　optimization　of　the　unit　cell　is　in　good　agreement　with　the　experimental　data.　Our　calculations　show　that　the　valence　band　maximum　(VBM)　and　conduction　band　minimum　(CBM)　are　located　at　G　resulting　in　a　direct　energy　gap.　The　optical　properties　are　analyzed,　and　the　independent　second　harmonic　generation　(SHG)　coefficients　are　determined.　By　an　analysis　of　the　band　structure,　we　can　get　that　SHG　response　of　the　system　can　be　attributed　to　the　transitions　from　the　bands　near　the　top　of　valence　band　that　are　derived　from　the　Se/Te　p　states　to　the　unoccupied　bands　contributed　by　the　p　states　of　In　atoms.