So　far,　little　attention　has　been　paid　to　the　vibration　analysis　of　multi-span　lattice　sandwich　beams,　particularly　using　the　assumed　mode　method　(AMM).　In　this　paper,　the　mode　shapes　of　multi-span　sandwich　beams　are　assumed　as　those　of　uniform　beams　modified　by　the　interpolation　functions.　The　equation　of　motion　of　the　beam　is　established　using　Hamilton＇s　principle.　The　natural　frequencies　of　multi-span　pyramidal　and　Kagome　sandwich　beams　so　calculated　agree　well　with　those　determined　using　the　ANSYS　software,　which　indicates　that　the　present　methodology　is　suitable　for　solving　multi-span　sandwich　beams　with　lattice　truss　cores.　The　effects　of　Young＇s　modulus,　damping　and　geometric　parameters　of　cores　and　sheets　on　the　natural　frequencies　and　time　domain　responses　of　two　kinds　of　multi-span　sandwich　beams　are　analyzed.　When　the　truss　radius　and　sheet　thickness　are　increased,　the　natural　frequencies　are　increased　initially　and　then　decrease,　while　the　vibration　amplitudes　at　the　mid-points　of　both　the　multi-span　pyramidal　and　Kagome　sandwich　beams　decrease.　With　the　increase　of　the　inclination　angle　of　the　truss　alpha(c),　the　natural　frequencies　of　structures　experience　a　slight　decline.　In　contrast,　the　amplitudes　at　the　mid-points　of　the　two　different　three-span　sandwich　beams　both　rise.