Catalytic reforming, which produces raw material of aromatic hydrocarbon and high-octane clean-gasolineblending component, is a principal technology. According to the content of platinum and tin loading on industrial reforming catalyst, platinum loading was kept constant at 0.6 Wt% and the amount of tin was varied from 0 to 1 Wt% in the catalysts. A series of Pt-Sn/Al2O3 reforming catalysts were characterized with in situ FTIR of adsorbed CO method which is established in this study. And the adsorbed CO infrared peaks were obtained at room temperature on Sn/Al2O3 catalysts that the mount of tin was under 1 Wt% in the first time. At room temperature the CO species of Pt sites adsorbed on the surface of Pt-Sn/Al2O3 reforming catalysts mainly on linearly-bonded CO species. It was found that there was a general trend that the amount of bridge-bonded CO species was decreasing and the amount of linearly-bonded CO species was increasing, with increasing amounts of tin in the catalyst. It was stated that the dispersity of platinum atoms was increasing. The temperature increasing desorption process was used to show that the CO band of Pt sites disappeared completely at 300 ℃ on 0.6%Pt/Al2O3, and the CO band of Sn sites disappeared completely at 120 ℃ on 0.3%Sn/Al2O3. The CO band of Pt sites and Sn sites disappeared completely at 350 ℃ on 0.6%Pt-0.3%Sn/Al2O3. Compared reforming catalysts Pt-Sn/Al2O3 with Pt/Al2O3, the linearly adsorbed CO band of Pt sites shift to high frequencies. This suggests that the electronic density of Pt increased due to the loading of Sn. Therefore, in situ FTIR is an effective tool for characterization of low metal reforming catalysts, which provides important information of interactions between tin and platinum.