The co-adsorption of hydrogen and CO on Pt film was studied by in-situ attenuated total reflection Infrared (ATR-IR) Spectroscopy. It was found that the adsorption of CO on Pt is much stronger than that of hydrogen, and the co-adsorbed hydrogen species lead to dramatic red shifts of both linear and bridged-adsorbed CO peaks. The more hydrogen species adsorbed on Pt surface, the more red shifts of CO frequencies were observed. Based on the results obtained from the well-designed experiments, it is deduced that H may act as an electron donor on Pt surface and negative charge is transferred from H to Pt. Thus, the surface charge properties of Pt film were changed, which enhances the d-pi* backdonation effect between Pt and CO and consequently leads to dramatic red shifts of CO peaks. The density functional theory (OFT) calculations based on simple models confirmed the charge transfer effect between hydrogen and Pt. This study also shows that ATR-IR technique is a powerful tool to investigate the gas-solid interface. Crown Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.