The effects of carbon monoxide and water on the adsorption and desorption of hydrogen on the surface of polycrystalline platinum foil have been studied using the technique of thermal desorption spectroscopy（TDS） under ultrahigh vacuum(UHV) conditions. The carbon monoxide preadsorbed on the surface of platinum at 310 K strongly prevents hydrogen from adsorbing on the platinum. As the coverage of carbon monoxide increases, the amount of hydrogen adsorption decreases. After the platinum surface is predosed with more than 20 L of carbon monoxide, the hydrogen adsorption is entirely blocked. Water gives no direct effects on the adsorption and desorption of hydrogen at 310 K. However, existence of water makes two new peaks(590, 790 K) appear on the hydrogen desorption spectrum. This is believed to be due to water-gas shift reaction between water in the system and carbon monoxide or carbon species deposited on the catalyst surface.