Mixed　traffic　is　a　significant　feature　of　Chinese　traffic　flow　on　urban　street　network,　which　is　also　a　major　cause　of　traffic　congestion　and　frequent　traffic　accidents.　In　sections　where　motor　vehicles　and　non-motor　vehicles　moving　in　same　direction　without　separation,　they　would　interfere　with　each　other.　This　interference　has　serious　impact　on　the　capacity　of　sections,　and　simultaneously　increases　the　accident　risk.　This　paper　analyzed　the　data　through　the　method　of　probability　theory　and　statistics,　and　got　the　result　that　＇the　number　of　non-motor　vehicles　and　the　lateral　distant　between　motor　vehicles　and　non-motor　vehicles　are　both　interference　factors　aroused　by　non-motor　vehicles＇.　Finally,　non-motor　vehicles＇　disturbance　model　to　the　motor　vehicles　were　set　up　based　on　data　analysis　and　proved　to　be　correctly.　The　research　provided　a　theoretical　and　basis　to　the　traffic　safety　management　under　the　mixed　traffic　environment.　©　2009　ASCE.