All-inorganic　double　perovskites　as　promising　photovoltaic　materials　have　received　great　attention　in　recent　years.　In　this　work,　the　structural,　mechanical,　electronic,　and　optical　properties　of　mixed-halide　double　perovskites　Cs2TiI6-xBrx　(x　=　0,　2,　4,　and　6)　were　studied　by　using　first-principles　calculations.　The　calculated　lattice　parameters　of　Cs2TiI6-xBrx　agree　well　with　the　reported　experimental　values.　The　calculated　results　have　confirmed　that　these　compounds　are　thermodynamically　stable.　Moreover,　these　mixed-halide　double　perovskites　can　easily　be　converted　into　thin　films　based　on　their　unique　mechanical　properties.　The　obtained　band　gaps　of　the　Cs2TiI6-xBrx　systems　using　the　PBE+U　method　have　better　matched　with　the　experimental　values.　When　the　Br　content　increases,　the　band　gap　of　Cs2TiI6-xBrx　increases　gradually,　which　leads　to　a　decreased　optical　performance　in　the　visible　light　region.　Based　on　a　suitable　direct　band　gap　and　strong　absorption　coefficient,　Cs2TiI2Br4　is　an　ideal　potential　material　for　single-junction　solar　cells.　This　journal　is　©　The　Royal　Society　of　Chemistry　and　the　Centre　National　de　la　Recherche　Scientifique.