Visual　and　real-time　plasmonic　metamaterial　biosensors,　relying　on　surface　plasmon　resonance　(SPR)　on　metallic　subwavelength　structures,　have　significant　potential　for　colorimetric　biochemical　sensing　by　simple　instrumentation　or　even　naked　eye.　In　this　paper,　we　present　a　visual　and　real-time　sensing　strategy　for　the　detection　of　the　biotin-avidin-system　(BAS),　which　is　a　powerful　tool　in　biological　sciences.　The　metamaterial,　consisting　of　an　array　of　three-dimensional　all-metal　nano-cavities,　can　confine　the　light　into　the　near　field　and　enable　strong　light-matter　interactions　there.　Therefore,　The　metamaterial　shows　significant　color　shifts　with　small　refraction　index　changes.　When　a　monomolecular　layer　of　thiolated　biotin　and　streptavidin　bonding　to　the　surface　of　the　nanostructure　successively,　the　color　of　the　metamaterials　changes　from　red　to　violet　and　then　loden.　This　sensing　strategy　offers　new　opportunities　for　convenient　detection　of　proteins,　nucleic　acids　and　lipids.