In　order　to　quantitatively　study　the　mechanical　characteristics　of　active　nodes,　load　tests　on　3　groups　node　whose　specimens　come　from　Beijing　subway　construction　site　are　conducted　in　laboratory.　The　load-deformation　(P-)　curve　and　failure　mechanisms　of　these　specimens　are　obtained,　based　on　which　the　bearing　capacity　and　stiffness　under　its　working　condition　are　thoroughly　analyzed.　By　comparing　the　bearing　capacity　and　the　stiffness　between　active　nodes　of　them　and　that　of　18,　20　and　24　m　steel　braces,　the　improvement　measures　to　enhance　the　mechanical　properties　of　these　active　nodes　are　put　forward.　The　results　show　that　the　mechanical　properties　vary　in　the　3　groups　with　different　active　nodes.　The　bearing　capacity　and　the　stiffness　of　the　specimen　with　the　bidirectional　wedge　are　stronger　than　that　of　the　specimen　with　the　unidirectional　wedge.　The　failure　mechanisms　of　single-box　active　node　include　the　yield　of　rib　in　the　middle　position　after　being　pressed,the　shearing　failure　of　the　weld　seam　between　the　rib　in　the　middle　position　and　channel　steel.　And　those　of　double-box　active　node　show　failure　modes　including　the　yield　of　rectangular-ambulatory-plane　section　of　the　movable　end　and　the　buckling　damage　of　lateral　walls　of　the　movable　end.The　overall　mechanical　properties　of　steel　braces　are　determined　by　the　active　node.　It　is　suggested　that　the　following　measures　to　enhance　the　be　aring　capacity　of　steel　brace　should　be　adopted:　improving　the　strength　of　steel　wedge,　strengthening　the　strength　of　weld　seam　between　the　rib　in　the　middle　position　and　channel　steel,　and　adopting　active　node　with　the　bidirectional　wedge.In　a　word,in　the　internal-shoring　retaining　structure　of　foundation　pit　engineering,the　active　node　is　the　weak　link　in　the　steel　bracing　system,　whose　bearing　capacity,　stiffness　and　emergency　capacity　are　insufficient,　thus　requiring　emphasis　and　improvement　measures.　©　2019,　Editorial　Department　of　Journal　of　Beijing　Jiaotong　University.　All　right　reserved.