The　planar　hybrid　metallic　microstructured　metamaterials　can　utilize　the　transverse　electromagnetic　resonance　coupling　effect　of　adjacent　resonant　units　to　enhance　the　absorption　bandwidth　(ABW),　which　is　widely　used　in　the　design　of　broadband　terahertz　(THz)　absorbers.　However,　it　is　difficult　to　further　broaden　the　ABW　since　only　a　limited　number　of　resonant　units　can　be　arranged　in　the　2-D　plane.　Here,　we　propose　a　pyramidal　3-D　metamaterial　absorber　that　increases　the　number　of　resonances　by　superimposing　metallic　dielectric　layers　with　different　sizes　in　the　vertical　direction.　Ultrawideband　wave　absorption　at　THz　frequencies　is　realized　by　longitudinal　electromagnetic　resonance　coupling　between　the　layers　of　the　metamaterial　structure.　The　results　show　that　the　3-D　metamaterial　achieves　more　than　90%　ultrabroadband　absorption　in　the　range　of　0.83-2.73　THz　with　the　relative　ABW　exceeding　106%.　In　addition,　the　equivalent　circuit　model　of　the　absorber　is　constructed　to　verify　the　simulation　results.　This　study　provides　a　novel　idea　for　the　design　and　processing　of　ultrawideband　THz　absorbers.