Abstract: The present application relates to the technical field of wastewater treatment and rapid pollutant detection, in particular to a chitosan-polyacrylamide composite porous hydrogel, preparation and use thereof, and a metal ion-adsorbing and detecting reagent and method. The chitosan-polyacrylamide composite porous hydrogel of the present application is prepared by in situ polymerization of a chitosan sol, an acrylamide, a crosslinking agent and a surfactant into a mixed solution comprising liquid droplets, followed by steps of curing, washing, and freeze-drying. The present application further provides a metal ion-detecting reagent, which is obtained by adsorbing a color developing agent into the chitosan-polyacrylamide composite porous hydrogel as described above, wherein the color developing agent is a dye that changes color when encountering metal ions. The chitosan-polyacrylamide composite porous hydrogel of the present application has balanced mechanical properties and porosity.