Weaving　sections　have　been　shown　to　have　a　great　effect　on　capacity　of　a　roundabout,　because　at　weaving　sections　the　traffic　conflict　and　interference　are　predominant,　resulting　in　a　reduction　of　speed　as　well　as　increase　of　gaps.　It　is　known　that　weaving　section　of　roundabout　is　the　bottleneck　of　the　traffic　movement.　Therefore,　it　should　be　given　the　highest　priority　in　the　capacity　analysis.　The　current　methods　of　estimating　the　approach　capacity　of　a　roundabout　mainly　utilize　information　of　vehicles　entering　and　exiting　the　roundabout.　From　literature　review　it　has　been　found　that　few　studies　are　conducted　based　on　the　traffic　characteristics　of　weaving　section　in　capacity　estimation.　The　purpose　of　this　research　is　to　estimate　the　capacity　of　roundabout　by　modeling　radius　of　roundabout,　width　of　circulating　roadway,　and　gap　acceptance　at　the　weaving　sections.　For　this　reason,　a　total　of　21　roundabouts　that　are　located　at　the　metropolitan　Beijing　are　selected　to　conduct　data　collection.　Significance　analysis　of　speed　at　weaving　sections　has　been　conducted　by　means　of　the　variance　analytic　method.　By　taking　geometric　conditions　and　traffic　conditions　into　account,　new　concepts　of　＂Quasi-saturation　state　of　roundabout＂　and　＂The　Capacity　of　Roundabout＂　are　introduced　in　this　study.　The　regression　models　of　the　headway　and　the　radius　on　both　the　outer　lanes　and　the　inner　lanes　are　established　respectively　using　Statistical　Program　for　Social　Sciences　(SPSS　18.0)　for　windows.　Moreover,　based　on　the　theory　of　saturation　flow　rate,　a　new　method　is　proposed　to　estimate　the　capacity　of　single-lane　and　multi-lane　roundabouts　using　MATLAB　software.　And　then　the　real　data　are　taken　to　validate　this　model.　The　findings　from　this　research　demonstrate　that　capacity　estimates　with　weaving　section　vehicles　result　in　improved　prediction　of　the　actual　capacity　of　a　roundabout.