The　auther　addressed　a　new　method　to　analyze　the　functions　of　the　road　network　using　Floating　Car　Data　(FCD).　The　tracking　data　of　GPS　equipped　and　saved　on　floating　cars　was　collected　and　matched　with　GIS　data　for　the　city.　It　shows　that　many　roads　with　high　level　functions　carry　lots　of　short　trips　and　the　detouring　rate　(actual　travel　distance　v.s.　direct　distance)　is　very　high　due　to　the　inadequate　functional　hierarchy　of　road　network　which　inflecting　the　performance　of　the　network.　The　author　also　gives　some　advices　directed　at　the　problems　mentioned　above.