Chromium　(Cr3+)　as　a　highly　toxic　pollutant　has　aroused　much　attention　due　to　its　wide　industrial　applications.　Covalent　organic　frameworks　(COFs)　have　been　considered　as　one　of　the　most　promising　metal　ion　sensors　due　to　their　open　pore　channels　and　abundant　adsorption　sites.　Herein,　a　novel　luminescent　one-dimensional　COF　(Py-An　COF)　was　constructed　by　the　condensation　of　5′-(anthracen-9-yl)-[1,1′:3′,1″-terphenyl]-4,4″-dicarbaldehyde　(An-2CHO)　and　1,3,6,8-tetrakis(p-aminophenyl)　pyrene　(PyTTA).　The　resulting　COF　showed　high　crystallinity,　comparative　high　surface　area,　and　good　thermal　stability,　which　can　be　utilized　for　Cr3+　fluorescent　sensors　with　high　sensitivity　and　selectivity.　Furthermore,　the　coordination　between　Schiff-base　N　atoms　and　Cr3+　inhibits　the　photoinduced　electron　transfer　(PET)　process,　resulting　in　the　enhanced　fluorescence　intensity　of　chromophores　(436　nm)　and　decreased　the　fluorescence　intensity　of　Py-An　COF　(512　nm)　simultaneously,　which　eventually　realizes　a　highly　efficient　ratiometric　fluorescent　sensor　for　trace　Cr3+.　Compared　with　other　porous　fluorescent　materials,　Py-An　COF　possesses　a　lower　detection　limit,　higher　sensitivity,　and　better　selectivity.　This　work　provides　strategic　guidance　for　the　design　of　COFs　as　ratiometric　fluorescence　sensors.　©　2023　American　Chemical　Society.