In　a　tilted　tunnel　fire,　the　inlet　air　velocity　caused　by　the　stack　effect　at　the　entrance　of　the　tunnel　would　be　beneficial　to　smoke　control　whether　the　longitudinal　ventilation　system　is　used　or　not.　This　paper　conducted　the　simulation　to　investigate　the　smoke　spread　behaviours　caused　by　fires　in　tilted　tunnels　with　natural　ventilation.　The　expression　of　the　smoke　back-layering　length　and　the　inlet　air　velocity　induced　by　fires　were　deduced　in　the　tilted　tunnel　fire　scenarios　by　the　method　of　dimensional　analysis.　The　effect　of　various　tunnel　slopes　(5-15%)　on　the　smoke　behaviours　characteristics　and　the　inlet　air　velocity　were　specifically　considered.　The　proposed　correlation　reveals　that　the　dimensionless　back-layering　length　is　independent　of　the　heat　release　rate　(HRR)　and　its　relationship　with　the　tunnel　slope　is　proportional　to　-1.96　power.　The　established　equation　reveals　that　the　dimensionless　inlet　air　velocity　is　proportional　to　0.31　power　of　the　dimensionless　HRR　and　it　increases　exponentially　with　the　tunnel　slope.　This　research　on　this　topic　may　contribute　to　optimize　the　application　of　natural　ventilation　systems　or　mechanical　ventilation　in　tilted　tunnels.