This　article　studied　the　absorbing　properties　of　three　dimensional　honeycomb-structured　absorbing　materials　based　on　the　Finite　Element　Method　(FEM)　with　periodical　boundary　conditions　(PBCs).　By　applying　the　PBCs　and　Floquet　theorem　of　two　dimensional　periodic　structures,　the　factors　that　affect　the　absorbing　performance　of　three　dimensional　honeycomb　structure　are　studied.　These　factors　include　the　height　and　thickness　of　honeycomb　and　the　conductivity　of　materials,　and　so　on.　Basing　on　the　studies,　the　optimal　three　dimensional　honeycomb-structured　absorbing　materials　are　achieved　which　have　best　absorbing　effectiveness　for　Ku-band　electromagnetic　waves.