As　long-span　cable-stayed　bridge　with　multi-tower　has　complex　mechanical　characteristics,　the　seismic　responses　are　quite　different　when　the　lightweight　composite　girder　is　adopted.　In　this　paper,　a　practical　project　is　taken　as　research　background　and　the　scaled　test　specimen　is　made,　which　is　three　towers　cable-stayed　bridge　with　span　of　616m.　The　shaking　table　tests　under　uniform　excitation,　multi-support　excitation　and　multi-dimensional　earthquake　excitation　are　carried　out　respectively.　Results　show　the　fundamental　mode　shape　is　coupled　vibration　of　middle　tower　in　longitudinal　direction　and　girder　in　vertical　direction.　Under　the　uniform　earthquake　excitation　in　longitudinal　direction,　the　seismic　responses　of　towers　and　girder　are　significant.　And　the　seismic　responses　of　middle　tower　are　more　disadvantageous　than　side　tower　under　earthquake　excitation　in　transverse　direction.　The　tests　under　multi-support　and　multi-dimensional　earthquake　excitations　indicate　that　wave　propagation　effects　on　seismic　response　can　not　be　ignored　and　the　combination　method　for　different　direction　effect　recommended　by　seismic　specification　is　verified.