Large-span　steel　structures　will　inevitably　cause　some　relaxation　under　the　influence　of　actual　engineering　operations　or　environmental　influences.　After　the　cables　are　loosened,　the　force　system　must　be　readjusted　to　a　new　equilibrium,　which　will　cause　the　internal　forces　of　the　members　increase　or　decrease,　and　affect　the　structural　safety.　The　designed　cable-truss　structure　with　a　span　of　6　m　as　the　object,　the　experiment　on　relaxation　of　cable　was　done.　A　study　was　made　of　the　influence　to　spoke　cable-truss　structure　when　different　cable　was　loosened.　It　is　concluded　that　the　effect　of　relaxation　on　the　loop　cable　is　most　obvious,　and　the　loop　cable　is　defined　as　the　relaxation　sensitive　component,　the　most　unfavorable　structure　occurs　when　all　the　lower　radial　cables　are　relaxed.　Based　on　the　reliability　theory,　the　influence　of　different　cable　tensions　on　the　reliability　of　the　spoke　cable　truss　structure　and　the　sensitivity　of　different　parameters　of　the　structure　were　obtained　by　the　response　surface　method　and　Monte　Carlo　method,　the　safety　assessment　could　be　performed　for　the　prestress　loss　of　the　spoke　cable　truss　structure.　©　2019,　Editorial　Department　of　Journal　of　Tongji　University.　All　right　reserved.