NOVELTY - The present invention provides a method for preparing a platinum catalyst on low chlorine, which comprises using an XC-72 carbon black with a high aspect ratio (250 m less than SP greater than 2 less than /SP greater than /g) as a carrier; adding pure water into the carbon black for dilution; preparing chloroplatinic acid (H2PtCl6) into a solution and slowly dripping the solution into the mixture; adding NaOH solution into the mixture to adjust the pH value of the mixture to 10.5; heating the mixture under continuous mixing overnight and adding a small amount of NaBH4 solution; performing a solid-liquid separation on the reaction mixture; and performing a hydrogen reduction treatment on the powder to obtain a product. Thus, upon completion of preparation of the catalyst, the by-products are salts which must be removed to reduce the amount of residual chlorine ions and avoid poisoning of the platinum catalyst. The chlorine removal process comprises: (1) diluting the product with a large amount of water and heating the resulting mixture; (2) performing an ultrasonic oscillation on the mixture at a power of 50W/L and a frequency of 43Hz; (3) performing a solid-liquid separation on the mixture to remove a large amount of salts and washing the solid with hot water; and (4) drying and grinding the solid to obtain a platinum catalyst on low chorine. A 20%Pt/C catalyst prepared according to the invention contains a residual chlorine ion content of less than 160ppm. A membrane electrode assembly (MEA) is prepared for testing. The polymer electrolyte is Nafion 115. The power measured under load is 0.78W/cm less than SP greater than 2 less than /SP greater than , which is superior in performance than the commercial 20% Pt/C catalysts prepared by A & B companies, which had a power measured under load of 0.70 and 0.66W/cm less than SP greater than 2 less than /SP greater than , respective, under the same test conditions. According to a chlorine removal process using ultrasonic waves according to the invention, the residual chlorine ions can be reduced to 160ppm after solid-liquid separation. Thus, a high performance metal catalyst can be produced according to the invention and is applicable on fuel cells.