Abstract: The invention provides a highly dispersed ultra-small size carbon-supported noble metal catalyst and a preparation method thereof. The preparation method comprises: Step S1, mixing a carbon material with a hydrogenated borophene dispersion, wherein in a mixed solution, a mass ratio of the carbon material to the hydrogenated borophene is 1:0.01-1, and then dispersing the activated carbon in the mixed solution sufficiently and uniformly to obtain a uniform carbon material-supported hydrogenated borophene dispersion; Step S2, adding an aqueous solution of a noble metal precursor to the uniform carbon material-supported hydrogenated borophene dispersion according to a mass ratio of the carbon material to the noble metal of 1:0.001-0.5, and fully stirring to obtain a suspension; and Step S3, filtering the suspension, and after treatment, to obtain the highly dispersed ultra-small size carbon-supported noble metal catalyst.