NOVELTY - Catalyst with gold nano core-shell structure comprises a core layer of polystyrene microsphere and a shell layer of gold nanoparticles, where the grain diameter of the core-shell structure catalyst is 175-350 nm.    USE - The catalyst is useful: as a fuel cell catalyst; and for water treatment and air purification.    ADVANTAGE - The catalyst has high catalytic activity due to the large specific surface area of the cores shell structure; saves the amount of noble metals in the catalyst; has uniform grain diameter distribution and high chemical stability; comprises easily available raw materials; and has simple preparation, and is suitable for large scale production.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for preparing the gold nano core-shell structure catalyst, comprising preparing polystyrene microspheres by emulsion polymerization, dissolving 0.015-0.025 g sodium dodecyl sulfate in deionized water, adding into a three-neck flask, introducing nitrogen gas and stirring for 10 minutes at a speed of 300 revolutions/minute, raising the temperature to 80 degrees C, adding 0.1-0.2 g potassium persulfate solution, and adding 3-5 g styrene and 0.08-12 mol/l n-butyl alcohol in a drop wise manner for 30 minutes, polymerizing at 80 degrees C for 3 hours, cooling by ice bath to room temperature to obtain polystyrene micro-spheres of 160-320 nm, (b) modifying the surface of polystyrene microsphere by taking a mixed solution of 30 g/l potassium dichromate and 60 ml/l concentrated sulfuric acid solution as a roughening agent of polystyrene microsphere for roughening treatment, preparing another mixed solution by mixing equal amount of sodium chloride, stannous chloride and palladium chloride with deionized water, carrying out activation treatment to polystyrene microsphere, and ultrasonically dispersing polystyrene microspheres, and (c) coating gold nanoparticles on the surface of the microspheres by chemical plating technique, dissolving 20 g sodium citrate, 1 g tartaric acid and 5 g ammonium chloride in 100 ml deionized water, adding 5 g chloroauric acid, 12 g sodium sulfite and 5 g sodium thiosulfate, mixing uniformly, adding ultrasonically dispersed polystyrene microspheres, stirring for 30 minutes, filtering and separating, repeatedly washing with water and ethanol, filtering, and drying under vacuum at 4 degrees C.