A　driver＇s　behavior　of　controlling　a　vehicle　will　be　influenced　if　the　sight　distance　is　insufficient.　Thus　it　causes　the　change　of　the　vehicle＇s　operating　speed　and　the　start　or　termination　of　the　overtaking.　Because　sight　distance　changes　with　the　road　traffic　condition　at　any　time　and　any　place,　most　simulation　software　does　not　consider　the　effect　of　sight　distance　on　vehicle＇s　speed　and　overtaking.　This　paper　propounds　a　way　and　automatic　calculation　procedure　for　sight　distance　to　different　road　alignment,　offers　some　help　to　simulate　the　real　traffic　flow　characteristic　according　to　the　sight　distance　in　the　simulation　system.