Some new chitosan-based fluorescent hydrogels have been successfully prepared by grafting coumarin derivatives onto chitosan via a Schiff base forming reaction or acid amine condensation reaction. It is worth noting that hydrogels synthesized by the Schiff base forming reaction can be used as a good fluorescent sensor for the selective recognition, detection and adsorption of Fe²⁺ ions in aqueous solution. Among them, the adsorption efficiency of 1 g of a fluorescent hydrogel to Fe²⁺ ions can reach 63.2 mg. In addition, after being further modified, hydrogels still retain the ability to identify and adsorb Fe²⁺. Therefore, this probe optimizes the synthetic route to chitosan-based fluorescent sensors and expands the practical application value of fluorescent hydrogels.