The　portable　and　instrument-free　sensing　device　for　quantitative　detection　is　of　significant　applications　in　resource　constrained　countries　and　regions.　Here,　a　colorful　height　readout　device　formed　by　agarose　hydrogel　doped　with　gold　nanobipyramids　(AuNBPs@AG)　is　developed　for　the　determination　of　hydrogen　peroxide　(H2O2)　content.　The　responsive　mechanism　is　based　on　H2O2　guided　etching　of　AuNBPs,　which　causes　the　plasmon-mediated　color　change　of　the　AuNBPs@AG　hydrogel　filled　in　plexiglass　tube　from　top　to　bottom.　We　demonstrate　the　height　of　color-changed　hydrogel　is　quantitatively　related　to　the　concentration　of　H2O2.　The　agarose　hydrogel,　as　the　carrier　material　for　loading　AuNBPs,　guarantees　the　stability　of　AuNBPs　and　promotes　the　separation　of　complex　samples.　The　method　shows　a　good　linear　relationship　in　four　ranges　of　H2O2　concentrations　of　20　−　100　μM,　200　−　1000　μM,　1　−　10　mM　and　10　−　100　mM.　Compared　with　previous　methods,　using　this　inexpensive　and　easy　to　operate　device　for　H2O2　detection　can　effectively　reduce　the　interference　of　the　color　background,　overcome　the　problem　of　the　nanoparticles　aggregation,　and　eliminate　the　need　for　expensive　and　sophisticated　detection　instruments.　The　practicality　of　the　method　is　demonstrated　via　the　analysis　of　commercial　products　such　as　contact　lens　solution　and　hair　dye　with　satisfactory　results.　Our　work　provides　a　novel　path　for　developing　the　height-readout　quantitative　devices　with　integrating　hydrogels　and　plasmonic　nanomaterials.　©　2021