NOVELTY - Purified multi-walled carbon nanotubes are obtained by suspending multi-walled carbon nanotubes in nitric acid, washing and drying, or placing multi-walled carbon nanotubes in air, soaking obtained nanotubes in hydrochloric acid, and drying. Obtained purified nanotubes, solvent and azodiisobutyronitrile are heated, washed, and dried to obtain nitrile group-modified carbon nanotubes. Obtained modified carbon nanotubes and ethanol solution or ethylene glycol solution of chloroplatinic acid are reacted in oil bath, filtered, washed, and dried to obtain nano platinum catalyst.    USE - Manufacture of nano platinum catalyst used for proton exchange membrane fuel battery.    ADVANTAGE - The method provides nano platinum catalyst having high productivity, catalyzing activity and scattering ability, and can be manufactured economically by simple method.    DETAILED DESCRIPTION - Purified multi-walled carbon nanotubes are obtained by suspending multi-walled carbon nanotubes in 40% of nitric acid, refluxing for 3 hours, filtering, washing using water, suspending in 95% ethanol solution, and drying at 80 degrees C, or placing multi-walled carbon nanotubes in air, processing at 350 degrees C for 1 hour, soaking the processed carbon nanotubes in 1 mol.L-1 of hydrochloric acid, ultrasonically treating for 3-5 hours, filtering, washing using water, and drying at 80 degrees C. The obtained purified multi-walled carbon nanotubes, solvent and azodiisobutyronitrile are added to a reactor, ultrasonically treated for 15 minutes, vibrated at constant temperature in water bath vibrator at 60 degrees C for 80 hours, filtered using vacuum filtering membrane, washed using absolute ethyl alcohol and tetrahydrofuran, and dried in vacuum dryer to obtain nitrile group-modified multi-walled carbon nanotubes. The mixing ratio of solvent, purified multi-walled carbon nanotubes, and azodiisobutyronitrile is 40-100 ml:1 g:10-30 g. The solvent is absolute ethyl alcohol and tetrahydrofuran. The obtained nitrile group-modified multi-walled carbon nanotubes are added to a container, and ethanol solution or ethylene glycol solution of chloroplatinic acid is added. The ultrasonic frequency in the reactor is controlled to 35 kHz, and mixture in the reactor is vibrated for 15 minutes. The mixture is heated in oil bath, refluxed for 3 hours, filtered, washed using deionized water, and dried in vacuum dryer to obtain nano platinum catalyst. The mass ratio of multi-walled carbon nanotubes with respect to content of platinum in ethanol or ethylene glycol solution of chloroplatinic acid is 0.1-1.8:1. The ratio of total content of alcohol with respect to nitrile group-modified multi-walled carbon nanotubes is 250-500 ml:1 g.