Fire　spread　between　vehicles　is　of　a　great　concern　in　a　tunnel　fire.　Longitudinal　ventilation,　which　is　commonly　used　for　the　smoke　control　in　tunnel　fire,　would　inevitably　affect　fire　properties　and　fire　spread　in　tunnel　at　the　same　time.　Such　effects　were　studied　using　model-scale　experiments　in　this　paper.　The　results　show　that　fire　spread　mostly　occur　due　to　the　flame　touching　arising　from　flame　tilting　under　longitudinal　flow.　Safety　spacing　should　be　kept　for　preventing　fire　spread　between　vehicles.　The　effect　of　longitudinal　ventilation　on　the　tem-perature　distribution　in　the　downstream　area　of　the　fire　source　is　found　mainly　limited　to　the　vicinity　of　the　fire　source.　Maximum　ceiling　temperature,　flame　tilt　angle　and　downwind　flame　temperature　under　longitudinal　ventilation　are　found　to　be　heavily　dependent　on　Fr　(Froude　number)　and　dimensionless　Q*　(Dimensionless　heat　release　rate).　The　formulas　of　flame　tilt　angle　and　mean　downwind　flame　temperature　were　developed　and　predicted　results　were　compared　with　those　in　modelling　experiments.