The　paper　uses　close-range　photogrammetry　method　to　collect　the　10154　data　records　of　vehicle　spacing　when　34　vehicles　pass　a　signalized　intersection.　Through　the　research　of　the　collected　data,　it　shows　that　vehicle　spacing　varies　as　well　as　inclines　to　some　stable　scope.　This　explains　the　drivers　of　following　vehicle　cannot　exactly　judge　the　vehicle　spacing　and　the　drivers　cannot　exactly　keep　the　strength　of　stepping　on　the　gas.　So　the　actual　vehicle　spacing　always　oscillates　near　the　expected　vehicle　spacing　and　seldom　maintains　the　expected　distance.　By　analyzing　collected　one-dimension　time　sequence　data　of　vehicle　spacing,　by　using　reconstitution　phase　space　method　and　calculating　Lyapunov　exponent,　the　chaotic　status　of　vehicle　spacing　when　vehicles　passing　the　signalized　intersection　is　proved　qualitatively　and　quantitatively.　Copyright　ASCE　2007.