More　and　more　urban　traffic　tunnels　are　built　to　mitigate　the　traffic　problems　in　some　large　cities　at　present　time.　Fire　safety　problems　are　more　import　due　to　the　large　daily　traffic　flow　in　these　kinds　of　tunnels.　Numerical　studies　on　the　fire　environment　with　different　fire　size　in　tunnels　with　or　without　slope　are　carried　out　by　FDS　in　this　paper.　Longitudinal　temperature　distributions　are　obtained.　Different　fire　behaviors　are　found　for　a　fire　occurring　in　a　lope　tunnel　or　in　a　normal　tunnel.　Due　to　the　stack　effect,　the　temperature　fields　in　a　slope　tunnel　are　not　symmetry,　hot　smoke　spreads　towards　the　top　exit,　and　the　spread　speed　is　much　faster　than　that　in　the　normal　tunnel.　This　might　be　dangerous　for　the　occupant＇s　evacuation.　Special　measures　should　be　taken　for　these　kinds　of　fire　conditions.