Multiple　modes　resonance　provides　the　possibility　of　broadband　filtering　and　has　great　potential　applications　in　terahertz　devices,　including　miniaturized　spectrometers,　hyperspectral　imagers　and　optical　switches　in　communication　systems.　However,　it　is　difficult　to　further　expand　the　bandwidth　range　due　to　the　inability　to　stack　an　infinite　number　of　resonant　structures　in　a　finite　space.　Here,　an　innovative　method　is　reported　for　manipulating　two　localized　surface　plasmon　polaritons　(LSPP)　modes　by　multiscale-coupled　plasmonic　fields　to　realize　broadband　filtering　at　terahertz　(THz)　frequencies.　The　interaction　between　two　LSPP　modes　was　verified　theoretically　and　experimentally,　exhibiting　a　prominent　Rabi　splitting　and　two　peaks　with　high　transmittance.　Particularly,　broadband　filtering　is　accomplished　by　utilizing　a　double-layer　structure　that　can　be　regarded　as　a　cavity　for　inducing　far-field　interference.　Experimental　result　demonstrates　that　the　maximum　transmission　range　of　the　bilayer　metamaterial　reaches　0.63　THz.　Besides,　the　two　wide　bands　can　be　integrated　into　one　broadband　through　near-field　coupling　effects.　The　integration　of　strong　coupling　and　far-field　interference　expands　the　transmission　range　of　the　double-layer　metamaterial,　further　enhancing　its　capability　for　broadband　filtering.　This　unique　approach　for　manipulating　multi-mode　plasmonic　coupling　forges　a　convenient　route　for　realizing　broadband　filtering.