In　this　study,　the　square　steel　tube　column　is　connected　by　bolted　flange　instead　of　traditional　welding.　For　multi-rise　structure,　tension,　bending　moment,　and　shear　force　may　act　on　the　connection　under　vertical　and　horizontal　loads.　To　investigate　the　mechanical　behavior　of　flange　connections,　full-scale　model　tests　and　finite　element　analyses　of　10　bolted-flange　joints　were　carried　out.　The　mechanical　properties　of　the　specimens　and　the　influence　of　the　flange　thickness,　flange　size,　and　bolt　hole　diameter　under　a　tension-bend-shear　combination　were　obtained.　The　size　of　the　bolt　hole　and　flange　has　little　effect　on　the　load-carrying　capacity　of　the　connection.　With　the　increase　of　the　thickness　of　flange,　the　flexural　rigidity　and　load-carrying　capacity　of　the　connection　increase　obviously,　and　the　yield　mechanism　of　the　specimen　changes　from　flange　yield　to　bolt　yield.　The　influence　of　the　axial　tension　ratio　on　the　bolt　tension　was　investigated　by　the　experiment-verified　finite　element　models.　The　axial　tension　ratio　is　the　value　that　the　axial　force　of　column　divided　by　the　cross-sectional　area　and　the　material　design　strength　of　the　column.　Increasing　the　axial　tension　ratio　may　increase　the　bolt　tension,　which　has　a　harmful　effect　on　the　bolts　at　the　tension　side　of　the　flange.　Using　yield　line　theory,　formulas　for　calculating　the　static　load-bearing　capacity　resisting　the　bending　moment,　shear　and　tension　were　deduced　and　verified　by　comparing　with　the　result　of　experiment　and　finite　element　analysis.