As　the　very　important　parts　of　the　expressway　system,　on　and　off　ramps　have　a　great　effect　on　the　operation　effect　of　expressways.　Once　congestion　occurs　at　on　and　off　ramps,　it　will　directly　affect　the　safety　of　the　expressway　and　vehicles.　So　this　paper　first　analyzes　the　location　design　of　on　ramps,　the　length　and　the　influences　on　the　expressway　running　state　of　off　ramp　downstream　traffic　state,　and　establishes　the　expressway　operation　models　based　at　on　and　off　ramps.　The　expressway　operation　models　include　off　ramp　delay　model,　on　ramp　delay　model,　expressway　delay　model　and　side　road　delay　model　under　the　influence　of　the　distance　between　on　and　off　ramp　and　traffic　volume.　At　the　same　time,　the　paper　analyzes　the　connection　between　the　traffic　operation　state　and　traffic　safety,　and　establishes　the　expressway　safety　model　based　on　congestion　degree.　Through　simulation　verification,　the　impact　of　on　and　off　ramp　on　the　security　of　the　expressway　is　analyzed.　In　the　simulation,　safety　rank　division　is　simulated　to　verify　and　safety　index　of　different　safety　ranks.　Finally　the　paper　concludes　that　the　delay　caused　by　traffic　of　the　on　and　off　ramps　can　decrease　the　safety　of　expressway.　©　by　Archives　of　Transport　at　Warsaw　University　of　Technology.