Metal-insulator-metal　(MIM)　multilayer　structures　as　representative　plasmonic　systems　have　been　widely　studied.　In　such　a　system,　the　metal　surface　can　sustain　bound　surface　plasmon　polaritons　(SPPs)　and　couple　the　SPPs　in　a　dielectric　cavity.　Herein,　a　novel　fabrication　process,　based　on　electron　beam　lithography　(EBL)　followed　by　electroplating　deposition　of　gold,　has　been　developed　to　form　longitudinal　metal-air-metal　structures.　The　structures　consist　of　a　suspended　top　film　of　gold　supported　by　an　array　of　gold　pillars　and　a　bottom　ultrathin　gold　film.　When　the　gap　of　the　two　gold　films　is　comparable　to　or　smaller　than　the　decay　length　of　the　interface　mode,　the　interaction　between　SPPs　gives　rise　to　coupled　modes　which　can　localize　the　light　into　the　insulating　layer　for　stronger　field　confine　and　light-matter　interaction.　This　structure　exhibits　vibrant　reflective　color　at　normal　incident　light　and　significant　color　varying　with　different　matter　filling　in　the　nano-cavity.　The　sensitivity　can　reach　269.8　nm/RIU　which　offers　great　potential　for　visual　and　real-time　biochemical　detection.