Atmospheric-pressure dielectric barrier discharge (DBD) cold plasma was employed to fabricate Pt/TiO2 photocatalyst using the mixture of Ar and H-2 as working gas. X-ray photoelectron microscopy (XPS) and transmission electron microscopy (TEM) measurements were used to characterize the Pt/TiO2 photocatalyst. The results showed that H2PtCl6 was completely reduced to metallic Pt nanoparticles when the treating time was increased to 6 min. In addition, the Pt/TiO2 photocatalyst prepared by atmospheric-pressure DBD cold plasma (Pt/TiO2-P) showed high dispersion and smaller size of Pt particles, and enhanced metal-support interaction. The photocatalytic degradation of methylene blue (MB) was chosen as a model reaction to evaluate the activity of the Pt/TiO2 photocatalyst. The apparent rate constant of 0.5 wt% Pt/TiO2-P for the MB photodegradation was 1.4 times higher than that over 0.5 wt% Pt/TiO2-C sample (prepared by thermal reduction method). This may be attributed to the smaller size and high dispersion of Pt particles, and the enhanced metal-support interaction in Pt/TiO2-P sample, which was consistent with the results of XPS and TEM. The influence of Pt content on photocatalytic activity of Pt/TiO2-P was investigated, and the highest apparent rate constant was obtained at 0.5 wt% Pt content. This was much lower than that prepared by conventional methods. Optical emission spectra (OES) were observed during the reduction process of Pt ions by atmospheric-pressure DBD cold plasma, and the reduction mechanism was further discussed.