In　the　paper,　the　external　cost　of　urban　expressway　transportation　was　analyzed　quantitatively　by　four　aspects,　including　traffic　congestion　external　cost,　traffic　accident　external　cost,　air　pollution　cost　and　noise　cost.　Besides,　the　main　road　of　the　3rd　east　ring　expressway　in　Beijing　is　taken　as　an　example　to　conduct　the　calculation　of　transport　external　cost　according　to　different　time　period.　In　addition,　the　variation　of　transport　external　cost　during　different　time　periods　in　a　day　was　analyzed　in　the　paper.　It　was　found　that　congestion　external　cost　takes　up　the　largest　part　of　total　external　cost.　With　the　increase　of　traffic　volume　and　decrease　of　average　speed,　congestion　external　cost　rises　sharply.