Herein, a novel fluorescent covalent organic framework (COF) and its luminescent sodium alginate based hybrid hydrogel were synthesized and applied to detect and adsorb eriochrome azo anionic dyes. Firstly, by optimizing a series of conditions affecting the crystallinity, a dual-emission fluorescence COF (TD-COF) with high crystallinity was synthesized at room temperature for the first time. TD-COF yielded remarkable fluorescence and adsorption properties; thus it can be employed as a dual platform for fluorescence sensing and adsorption of eriochrome black T, eriochrome blue-black R and eriochrome blue SE. The platform showed good linearity in fluorescence detection of three dyes from 0 to 100 μg mL−1 and the maximum adsorption capacities ranged from 89.28 to 228.64 mg g−1. Subsequently, TD-COF had a Thiol-ene "click" reaction with thiolated sodium alginate to produce a sort of luminescent hybrid hydrogel material (GelTSA@TD-COF), which improved the maximum adsorption capacities of eriochrome blue-black R (6410.06 mg g−1) and eriochrome blue SE (106.79 mg g−1). Due to the blocky appearance of GelTSA@TD-COF, it is more portable and practical compared to powdered TD-COF, and can be used for on-site fluorescent visualization of dyes. Finally, the detection and adsorption effect of dyes in water samples further verified the practical application value of TD-COF and GelTSA@TD-COF.