The　main　geometrical　features　of　horizontal　jet　fire　with　rectangular　source　fuel　have　seldom　been　revealed　in　the　past,　especially　the　rectangular　orifice　with　same　area　but　different　aspect　ratios.　In　order　to　better　understand　the　rectangular　jet　fire,　a　set　of　numerical　simulations　were　carried　out　by　rectangular　source　fuel　with　same　rectangular　orifice　area　S　(4　cm(2))　but　different　aspect　ratios　(orifice　length　to　orifice　width:　L/W　=　1,　2,　4)　to　investigate　the　flame　shape,　flame　length　and　flame　width.　The　simulated　flame　lengths　and　flame　widths　were　compared　with　previous　experimental　data　and　calculated　values　using　the　Thornton　model.　The　non-dimensional　flame　length　and　flame　width　were　defined,　in　which　the　flame　geometrical　features　were　found　in　relation　to　the　orifice　aspect　ratio　and　fuel　jet　velocity.　Results　show　that　the　flame　length　and　flame　width　increases　with　fuel　jet　velocity,　while　the　flame　length　decreases　with　aspect　ratio　n　for　same　orifice　area,　but　the　flame　width　increases　simultaneously.　The　simulated　data　agree　well　with　previous　experimental　data,　but　the　predictions　by　Thornton　model　are　larger　than　simulated　and　previous　experimental　values.　The　modified　Thornton　model　is　proposed　considering　both　orifice　shape　and　aspect　ratio　to　apply　to　rectangular　jet　fire.　(C)　2017　Energy　Institute.　Published　by　Elsevier　Ltd.　All　rights　reserved.