Abstract: As the main component of the train body structure, the truss-cored flat panel is situated close to the wheel-track noise source and has a large area for noise radiation, and its acoustic performance directly influences the riding comfort of trains. This paper first establishes the wavenumber finite-element model and a sound-insulation prediction model for an aluminum truss-cored train floor using wavenumber finite elements and boundary integral equations. The wavenumber, transmission loss, and eigenvectors of the structure are calculated. The dispersion characteristics, sound-insulation performance and cross-sectional wave-modes of elastic waves are studied. The calculated results are compared with the prediction given in the references to verify the proposed model. Furthermore, this paper investigates the effects of the core layer's topological geometry of the extruded panel on the sound-insulation characteristics of aluminum extruded panels. The results show that varying the topological configuration of the core layer significantly changes the variation pattern of dispersion curves of elastic waves, which affects the sound-insulation properties of aluminum extruded panels. By comparing the topologies of classic extruded structures, it is found that the ‘herringbone’ ribbed plate structure has a relatively higher sound-insulation level and lower mass. This study can provide a reference for designing quiet and lightweight extruded panels.