Though　lightweight　sandwich　structures　have　been　extensively　applied　in　practical　engineering,　it　remains　a　challenge　to　control　wave　propagation　and　vibration　in　these　structures　in　a　low-frequency　range.　In　this　work,　the　band　structure　of　flexural　waves　in　a　metamaterial　sandwich　beam　(MSB)　with　hourglass　lattice　truss　core　is　investigated　using　the　transfer　matrix　method　(TMM).　The　hourglass　truss　structure　with　lumped　masses　is　modelled　as　a　series　of　local　resonators　with　determined　equivalent　stiffnesses　and　masses.　A　metamaterial　dual-beam　(MDB)　model　is　then　established　to　describe　the　MSB,　and　the　MDB　model　is　noted　to　be　equivalent　to　the　conventional　metamaterial　beam　(CMB)　model　under　base　excitation.　The　MSB　is　further　studied　directly　by　the　finite　element　method　that　confirmed　the　MSB　can　be　represented　by　the　CMB　through　the　transmittance　analysis　and　band　structure　analysis.　Subsequently,　parametric　study　is　performed　to　investigate　the　effects　of　the　material　and　structural　parameters　on　the　band　structures　of　the　MSB.　This　work　provides　a　roadmap　of　modelling　of　lightweight　lattice　sandwich　beams　with　complex　core　structures　and　presents　guidelines　for　applying　sandwich　beams　to　control　wave　propagation.　©　2021　Elsevier　B.V.