The invention discloses a method for preparing a platinum-doped carbon nanotube. The method comprises the steps as follows: after dissolving a single-walled carbon nanotube in an acid solution, extracting the carbon nanotube in the acid solution; adding the carbon nanotube and chloroplatinic acid into an organic solution of an alkali, and subjecting the obtained alkaline solution of the carbon nanotube to microwave heating; centrifuging the alkali solution of the carbon nanotube after microwave heating; and drying the alkali solution of the carbon nanotube after centrifugation to obtain the platinum-doped single-walled carbon nanotube. According to the method, a microwave heating process is introduced for reducing chloroplatinic acid, the heating is fast and uniform, and the process of obtaining platinum nanoparticles is shortened to a large extent due to the characteristics of safety and simplicity.