The present invention relates to a method for synthesizing highly dispersed supported platinum catalyst. More particularly, the present invention relates to a method of synthesizing highly dispersed supported platinum catalyst comprising: dissolving a reducing agent in a solvent to produce a solution, dissolving a platinum chloride to the same solvent; adding a carbon support and platinum in a predetermined ratio to the above mixed solution, agitating the mixture, performing ultrasonic treatment, and performing heat treatment; and adding a HCl solution, agitating the mixture, separating the precipitates via filtration to produce a catalyst, and then washing the catalyst with distilled water, thereby obtaining an active highly dispersed supported platinum catalyst which has excellent electric charge activity, uniformly-sized platinum particles and relatively high specific surface area.