In　order　to　guarantee　the　construction　safety　during　the　flat　rotation　process　of　rotary　structures,　a　method　was　proposed　to　monitor　the　stability　of　the　structures　in　real　time　by　measuring　the　vibration　acceleration　of　the　rotary　structure.　First,　the　vibration　data,　collected　during　flat　rotation　of　a　high-speed　railway　bridge　structure,　were　compared　with　the　result　of　finite　element　modality　analysis.　The　result　showed　that　the　vibration　in　elevation　of　rotary　structure　was　mainly　influenced　by　the　first　three　order　vibration　modes　in　elevation,　and　the　pier　bending　moment　related　to　stability　was　only　affected　by　the　two　asymmetrical　vibration　modes.　Then,　the　analytic　formula　of　the　ratio　of　vibration　acceleration　and　pier　bending　moment　for　the　rotary　structure　was　deduced　under　the　condition　when　the　rotary　structure　was　vibrating　in　single　asymmetrical　vibration　mode.　Verified　by　finite　element　modeling,　the　analytic　formula,　considering　cantilever　beam　as　infinite　degree　of　freedom　straight　rod　and　pier　as　the　lumped　mass　matrix　beam　element,　can　describe　the　relationship　between　vibration　acceleration　and　pier　bending　moment　within　the　range　of　the　engineering　allowable　error　when　the　rotary　structure　was　vibrating　under　specified　vibration　mode.　Finally,　the　vibration　of　rotary　structure　was　simplified　as　the　superposition　of　the　first　two　asymmetrical　vibration　modes　in　elevation　of　rotary　structure.　The　recommended　formula　of　permissible　value　of　vibration　acceleration　for　passenger　dedicated　line　bridges　is　given,　to　provide　a　reference　for　similar　projects.　©　2016,　Science　Press.　All　right　reserved.