The　mechanical　properties　of　foam　concrete　are　significantly　affected　by　its　failure　mode,　closely　related　to　its　density　and　height-diameter　ratio,　and　unfavorable　failure　mode　would　inevitably　adversely　affect　its　mechanical　performance.　To　investigate　the　effect　of　density　and　height-diameter　ratio　on　the　failure　modes,　firstly　a　quasistatic　compression　test　is　carried　out　on　the　specimens　with　four　densities　(400,　600,　800,　and　1000　kg/m3)　and　four　height-diameter　ratios　(0.5,　1.0,　1.5,　and　2.0).　Most　specimens　exhibit　unfavorable　splitting　failure,　while　only　the　specimens　with　low　densities　or　small　height-diameter　ratios　undergo　crushing　or　shear　failure.　To　improve　the　mechanical　performance　of　foam　concrete,　especially　the　energy　absorption　capacity,　measures　including　layered　architecture,　density　gradient,　and　split　plate　are　proposed　and　experimentally　examined　in　the　present　study.　The　results　show　that　sufficient　density　difference　between　adjacent　foam　concrete　layers　is　able　to　effectively　mitigate　the　propagation　of　cracks　so　as　to　significantly　improve　its　mechanical　performance.　Moreover,　steel　split　plate　at　the　interface　of　adjacent　foam　concrete　layers　is　capable　of　successfully　stopping　crack　development　among　different　layers,　demonstrating　superior　energy　absorption　capacity.　In　addition,　layer　by　layer　crushing　failure　mode　can　be　achieved　through　the　synergy　of　density　gradient　and　split　plates　to　fill　the　demand　of　multi-level　protection　for　important　structural　members.