To　study　the　mechanical　behavior　of　rectangular　hollow　section　(RHS)　steel　tube　joints　with　concrete　filled　in　chords,　mechanical　behavior　of　compression,　tension　and　bending　are　analyzed　in　this　paper　and　compared　with　RHS　steel　tube　joints.　The　results　show　that　concrete　filled　in　chord　can　improve　the　mechanical　behavior　of　joints.　It　can　obviously　enhance　the　ultimate　bearing　capacity　and　rigidity　of　compression　joint,　and　the　failure　mode　of　compression　joints　is　local　transverse　compression　failure.　It　does　not　have　much　effect　on　the　ultimate　bearing　capacity　of　tension　joints,　but　can　enhance　the　rigidity　of　joints;　and　it　can　change　the　range　of　geometric　parameters　of　failure　mode:　the　failure　modes　of　tension　joint　are　punching　failure　mode,　effective　width　failure　mode　and　flange　yield-line　failure　mode.　The　bending　rigidity　and　ultimate　bending　capacity　of　joints　are　greater　than　RHS　steel　tube　joints,　and　the　failure　mode　of　bending　joints　is　considered　as　tension　flange　effective　width　failure　mode　of　branch　tube.　The　bearing　capacity　formula　for　three　types　joint　are　recommended　according　to　its　failure　modes.