A method for supporting nano-sized platinum particles in the highly dispersed state is provided to improve the performance of the fuel cell electrode as a method for preparing a platinum-supported carbon nanotube catalyst used for a material of a fuel cell electrode. A preparation method of a platinum catalyst supported on carbon nanotube by chemical vapor deposition comprises: a pre-treatment step of heat-treating a carbon nanotube, treating the heat-treated carbon nanotube with a hydrochloric acid solution and a sulfuric acid-nitric acid mixed solution to remove impurities from the carbon nanotube, and replacing an oxidation group on the surface of the carbon nanotube; a vaporizing step of using a methyltrimethylcyclopentadienyl platinum as a platinum precursor, injecting the methyltrimethylcyclopentadienyl platinum into a vaporizer, and heating the methyltrimethylcyclopentadienyl platinum to a temperature of from 60 to 80 degrees to vaporize the methyltrimethylcyclopentadienyl platinum; and a supporting step of installing the carbon nanotube within a reactor, and supporting platinum particles onto the surface of the carbon nanotube by increasing temperature of the reactor while flowing nitrogen preheated to from 60 to 80 degrees passing through the vaporizer together with additional oxygen through the reactor, wherein the supporting step is conducted by controlling the reactor temperature to from 80 to 240 degrees, using nitrogen, a mixed gas of nitrogen and oxygen, or a mixed gas of nitrogen and hydrogen as a reaction gas, and controlling pressure to from 5 to 10 torr.
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