A simple and green method of modified multi-wall carbon nanotubes (MWCNTs) by methylene blue under ultraviolet irradiation was reported. The irradiation time, methylene blue dosage and ultraviolet wavelength were considered as the three main factors. The different factors of functionalized MWCNTs and their catalytic performance were systematically studied. TEM was used to indicate the catalyst morphology. Cyclic voltammetric and chronoamperometric experiments were used to study catalytic activity and stability for methanol in alkaline solution. The results showed that the optimal conditions of irradiation time, methylene blue dosage and ultraviolet wavelength are 6 h, 10 mg and 254 nm, respectively. Under these conditions, catalyst has the best dispersion of Pt nanoparticles on the surface of functionalized MWCNTs, realizing the best catalytic performance, with catalytic activity at 2-fold of that of the commercial Pt/C catalyst. This modification of MWCNTs provides a new way for achieving anode catalysts with high activity and low cost in the fuel cells.