Filling　with　concrete　will　eliminate　or　delay　the　local　buckling　of　steel　hollow　sections,　and　will　increase　the　ductility　of　the　section　significantly.　Based　on　the　mechanic　model　for　the　analysis　of　bending　moment　versus　curvature,　the　hysteresis　load　versus　deflection　relations　are　analyzed　in　this　paper.　The　theoretical　results　show　good　agreement　with　those　of　the　tests.　Influences　of　several　parameters,　such　as　axial　compression　ratio,　slenderness　ratio,　steel　ratio　and　strength　of　the　materials　on　the　hysteresis　behavior　of　the　beam-columns　are　analyzed.　Finally,　simplified　calculating　method　for　the　model　of　restoring　force　and　the　ductility　coefficient　is　suggested.