Physical　parameters　such　as　structural,　mechanical,　electronic,　optical　and　thermoelectric　of　lead　(Pb)　free　halide　double　perovskites　(DPs)　Na2InBiX6　(X　=　Cl,　Br　and　I),　are　investigated　using　density　function　theory　(DFT).　Generalize　gradient　approximation　(GGA)　with　Perdew　Burke　Ernzerhof　(PBE)　exchange　correlation　functional　is　used　to　find　stable　structural　parameters.　To　calculate　correct　band　gap,　electronic　band　structures　and　density　of　states　(DOS)　are　evaluated　using　both　GGA-PBE　and　a　hybrid　functional　HSE06.　The　optical　and　mechanical　behavior　is　also　evaluated　for　the　considered　materials.　From　the　analysis　of　optical　parameters,　it　is　found　that　the　absorption　maximum　peaks　of　the　photon　energy　occurred　in　the　visible　and　ultra　violet　(UV)　region.　The　large　absorption　coefficient　and　higher　dielectric　constant　made　these　DPs　promising　candidates　for　optoelectronics.　The　analysis　of　mechanical　parameters　revealed　that　these　materials　are　stable.　Thermoelectric　parameters　i.e.　thermoelectric　parameters,　Seebeck　coefficient,　figure　of　merit,　power　factor,　electrical　conductivity,　carrier＇s　concentration　and　thermal　conductivity　are　also　calculated　and　discussed.