Using　theoretical　vibration　analysis　and　modal　experiment　investigation,　base　on　LabVIEW　soft,　this　paper　exploits　a　dynamic　test　system　which　can　sweeping　quickly　and　accurately　measuring　multi-DOF　system＇s　natural　frequencies　and　mode　of　vibration,　according　to　practical　engineering　-　combination　of　three　sections　of　beams,　had　tested　for　its　modal　analysis.　Experimental　results　show　that　experimental　modal　obtain　accurate　and　reliable　data,　have　a　high　practical　value.　©　2010　IEEE.