Numerical　investigation　was　carried　out　to　study　the　ceiling　gas　temperature　distribution　under　the　combination　effect　of　tunnel　slope　and　longitudinal　fire　location　in　a　naturally　ventilated　tunnel.　Results　show　that　in　horizontal　tunnel　with　fire　located　in　the　tunnel＇s　longitudinal　center,　the　ceiling　gas　temperature　is　symmetric　distributing　in　upstream　and　downstream.　With　fire　moves　to　the　right　(downstream)　portal,　the　ceiling　gas　temperature　in　upstream　tunnel　decays　faster　than　that　in　downstream,　and　vice　versa.　For　inclined　tunnels　(going　uphill),　the　ceiling　gas　temperature　is　asymmetrically　distributed　even　the　fire　is　located　in　the　longitudinal　center.　Interestingly,　with　fire　moves　to　downstream,　it　would　become　symmetric　again　and　then　it　returns　to　asymmetric.　Therefore,　the　tunnel　slope　and　the　longitudinal　fire　location　have　complex　combination　effect　on　the　ceiling　gas　temperature　distribution.　More　interestingly,　with　the　fire　moving　from　upstream　to　downstream　in　an　uphill　tunnel,　the　evolution　of　maximum　ceiling　gas　temperature　shows　two　tendencies,　depending　on　the　tunnel　slopes.　For　smaller　tunnel　slopes,　the　maximum　ceiling　gas　temperature　first　increases　and　then　decreases,　while　it　increases　monotonically　for　larger　tunnel　slopes.　Consequently,　the　critical　tunnel　slope　for　the　change　of　two　tendencies　was　proposed,　which　shows　the　variation　of　the　relative　strength　of　the　two　effects.　For　tunnel　slopes　lower　than　the　critical　value,　the　two　effects　are　comparable.　For　tunnel　slopes　larger　than　the　critical　value,　the　tunnel　slope　is　the　dominant　effect.　In　addition,　the　empirical　equation　of　offset　distance　was　proposed　as　intermediate　variable　to　characterize　the　combination　effects　on　the　maximum　ceiling　gas　temperature.　By　taking　the　absolute　value　of　offset　distance　as　characteristic　parameter,　the　predicting　equation　for　the　maximum　ceiling　gas　temperature　was　proposed.　©　2025　Elsevier　Ltd