The　construction　of　urban　underground　road　can　effectively　alleviate　the　increasingly　crowded　urban　traffic　conditions.　But　due　to　urban　traffic　characteristics,　the　treatment　of　vehicle　emissions　cannot　simply　copy　the　existing　highway　design　code.　Grasping　the　emission　characteristics　of　the　major　pollutants　of　motor　vehicles　in　the　urban　underground　road　has　a　very　important　guiding　significance　to　urban　tunnel　ventilation　system　design　criteria　and　design　method.　Taking　the　first-tier　cities　like　Beijing　and　Shanghai　and　the　second-tier　cities　like　Wuhan,　Nanjing　and　Guangzhou　as　objects,　through　inspecting　the　motor　vehicle　population,　vehicle　type,　traffic　flow,　speed　and　other　parameters,　the　influences　of　different　urban　traffic　characteristics　on　the　vehicle　emission　factors　were　analysed.　The　results　can　provide　the　basis　for　the　further　determination　of　pollutant　emission　factors　and　lay　down　the　foundation　for　the　tunnel　ventilation　design.