Density　functional　theory　(DFT)　based　on　the　plane　wave　basis　set　was　used　to　investigate　the　geometries,　electronic　structures,　and　linear　and　second-order　nonlinear　optical　properties　of　a　series　of　AgGa(S1-xSex)(2)　solid　solutions　with　chalcopyrite　structures.　The　compounds　showed　similar　band　structures,　and　band　gaps　decreased　with　increasing　x　value.　When　22.56%　Hartree-Fock　exchange　was　employed,　the　solid　solution　band　gaps　predicted　by　hybrid　PBE　functionals　were　consistent　with　experimental　values.　The　optical　properties　of　AgGa(S1-xSex)(2)　solid　solutions,　including　refractive　index,　birefringence,　reflectivity,　adsorption　coefficient,　and　second　harmonic　generation　coefficient,　changed　regularly　with　composition.　The　range　of　variation　was　between　that　for　AgGaS2　and　AgGaSe2.　The　results　indicated　that　crystals　with　specialized　optical　performances　could　be　designed.