The invention discloses an antibacterial agent containing serratia-marcescens metabolite prodigiosin and a preparing method. A methanol solution of the prodigiosin is added into a glycolic acid watersolution through a polytetrafluoroethylene hollow fiber membrane under the pressure effect, and the prodigiosin is evenly dispersed in an ultrafine-particle manner to form suspension; then the suspension and pregelatinized starch dispersed in a waterborne system are subjected to mixing ball milling, and through the adhesive effect of the pregelatinized starch, it is further promoted that the prodigiosin stably exists in the water environment; finally, polyvinyl-alcohol hollow microspheres are introduced, high-pressure homogenization treatment is conducted, then freezing, heating and drying areconducted, rich porous structures are formed, and microorganisms including bacteria are attracted and gathered, and the prodigiosin can fully play the bactericidal effect. According to the antibacterial agent containing serratia-marcescens metabolite prodigiosin and the preparing method, a bactericide obtained with the method can play the excellent bactericidal effect in an aquaculture system.