In　freeway　simulation,　the　operation　speed　model　is　key　to　the　reality　of　simulation.　The　operation　speed　is　related　to　traffic　and　road　conditions,　the　type　of　vehicle　and　its　performance.　The　road　conditions　refer　to　the　radius　of　curve,　the　road　cross-section,　the　grade　and　length　of　slope,　and　the　combination　of　the　curves　and　the　slopes.　In　order　to　build　a　suitable　simulation　model,　the　free　traffic　flow　speed　model　of　freeway,　based　on　the　extensive　and　field　investigation　of　different　freeways　in　China,　is　introduced　as　the　free-flow　speed　model　for　the　freeway　simulation　program.　In　simulation,　similar　freeway　is　input　according　to　actual　freeway　conditions,　and　the　operation　speed　is　selected　as　the　evaluation　index.　After　a　series　of　run,　the　statistic　result　is　get.　And　the　result　indicates　that　the　measured　data　and　the　expected　data　fit　well.　Copyright　ASCE　2007.