According　to　the　expressway　alignment　spatial　geometric　properties,　and　adopting　the　calculation　method　of　spatial　curvature　from　higher　mathematics,　authors　calculated　the　spatial　curvature　of　the　alignment　combining　with　the　expressway　plane　and　vertical　curve　combination　method,　and　modified　it　based　on　operating　speed.　According　to　the　modified　spatial　curvature　index,　different　operation　characteristics　and　distributions　of　the　vehicles　in　expressway　and　the　correlation　analysis　between　them　and　operation　safety,　combining　occupancy　of　passenger　car,　a　series　of　the　spatial　curvature　index　models　focused　on　the　operating　status　of　expressway　section　were　established.　Through　the　regression,　the　relevance　between　the　model　and　the　accident　ratio　was　analyzed　and　the　operating　speed　of　expressway　was　established.　Results　show　that　parts　of　spatial　curvatures　have　good　relevance　with　accident　ratio.　The　proposed　model　can　provide　theoretical　reference　for　highway　alignment　design.