The　cable　and　the　tension　bar　which　belong　to　the　basic　frame　member　of　the　prestressed　long-span　steel　structure　system　are　high　strength　steel　members　which　had　been　subject　to　cold-work　hardening　and　hot　rolling　and　modified　treatment　separately.　After　modifying,　the　members＇　strength　increased　significantly　and　their　ductile　nature　reduced　greatly.　Large　deformation　collapse　buckling　limiting　state　of　the　prestressed　long-span　steel　structure　system　is　the　controlling　factor　of　the　structure　security.　So　it　is　very　important　to　analyze　the　ductile　nature　of　the　cable　and　tension　bar　for　the　design　of　the　prestressed　long-span　steel　structure　system.　This　paper　takes　the　suspend-dome　of　the　badminton　gymnasium　for　2008　Olympic　Games　for　example,　attempting　to　analyze　and　study　the　stress　and　the　distort　ability　of　the　cable　and　the　tension　bar　under　severe　earthquake　and　overall　buckling.　The　study　indicates　the　mechanical　behavior　of　suspend-dome　structure,　i.e.　large　deform　in　system,　small　strain　in　cable　and　bar.　It　proves　that　the　cable　and　bar　with　low　ductility　capability　is　safe　to　be　applied　on　suspend-dome　structure　system.