This　paper　investigates　the　vibration　modal　experiments　and　the　modal　interactions　for　a　large　space　deployable　antenna　with　the　ring-truss　structure.　The　reduced　scale　model　of　the　large　deployable　ring-truss　antenna　is　firstly　introduced　briefly.　The　reduced　experimental　scale　model　of　the　ring-truss　structure　is　designed　and　is　manufactured.　The　experimental　measurements　of　the　vibration　modals　are　carried　out　for　reduced　scale　model　of　the　ring-truss　structure.　The　natural　frequencies　and　the　corresponding　modal　shapes　are　obtained　for　the　reduced　scale　model　of　the　ring-truss　structure.　The　forced　vibration　experiments　of　the　reduced　scale　model　are　also　finished　for　the　ring-truss　structure.　The　displacements　of　the　joint　point　under　different　excitation　frequencies　are　obtained　and　are　analyzed.　A　finite　element　(FE)　analysis　is　finished　for　the　reduced　scale　model　of　the　ring-truss　structure　through　applying　Nastran.　The　results　of　the　finite　element　method　(FEM)　verify　the　dynamic　behaviors　of　the　experimental　model.　The　modal　results　of　the　vibration　experiments　are　compared　with　those　of　the　theoretical　analysis　and　are　indicated　to　be　at　a　good　agreement.　The　phenomena　of　the　energy　transfer　are　observed　from　the　low　frequency　modal　vibration　to　the　high　frequency　modal　vibration　in　the　forced　vibration　experiments.　We　also　find　these　phenomena　in　the　process　of　studying　the　theoretical　model　for　the　ring　truss　antenna.　It　is　demonstrated　that　there　exist　the　phenomena　of　the　energy　transfer　from　the　low　frequency　mode　vibration　to　the　high　frequency　mode　vibration　for　the　ring　truss　antenna　when　the　excitation　frequency　is　consistent　with　the　lower　order　frequency　of　the　vibration.