The　paper　proposes　a　modeling　method,　which　is　called　Dynamic　Graph　Hybrid　Automata　(DGHA),　to　describe　the　evolution　law　of　traffic　flow　over　a　road　network.　In　the　model,　the　traffic　dynamics　are　described　by　the,　Modified　Cell　Transmission　Model　(MGM),　where　the　cells　are　expressed　by　hybrid　automata,　and　multi　-mode　switching　expressions　are　introduced　to　the　connections　among　these　cells.　The　proposed　DGHA　models　are　modularized　and　easily　-extensible,　and　are　implemented　by　Modelica　language　on　the　OpenModelica.　By　using　the,　modeling　method,　one　can　establish　traffic　flow　network　models　with　any　topology　structure.　Two　simulation　examples　show　the　effectiveness　of　the　proposed　modeling　method.