Lattice　Boltzmann　method　(LBM)　scheme　is　adopted　to　simulate　the　heat　transfer　processes　inside　isolated　phase　and　three-phase　enclosure　gas　insulated　switchgear　(GIS)　capsules.　D2Q9　fluid　flow　and　thermal　Lattice　Boltzmann　equations　(LBEs)　are　solved　through　streaming　and　collision　processes.　Buoyancy　force　driven　by　natural　convection　is　considered　by　the　Boussinesq　model.　Power　losses　and　thermal　boundary　conditions　are　obtained　from　closed　formulas.　Numerical　results　by　LBM　simulations　are　compared　with　those　from　physical　experiments　and　conventional　CFD　simulations.　Results　show　that　LBM　scheme　could　provide　a　simple　and　efficient　alternative　tool　in　the　flow-thermal　simulation　of　GIS　equipment　with　desirable　accuracy.　Thermal　performances　of　GIS　capsule　filled　with　different　insulation　gas　mixtures　(SF6,　N2,　CF4,　CO2,　CF3I)　are　then　analyzed.　Results　show　that　upper　conductors　of　three-phase　GIS　has　larger　temperature　rise　than　lower　conductor　due　to　the　natural　convection　effect.　Conductor　temperature　rise　inside　gas　mixture　increases　with　the　increase　of　second　gas　(N2,　CO2,　CF4)　fraction.　The　thermal　performance　of　GIS　capsule　could　be　reduced　with　the　presentation　of　insulation　gas　mixtures.　©　2021　International　Association　for　Mathematics　and　Computers　in　Simulation　(IMACS)