Silver foils irradiated by atomic oxygen (AO) generated in a ground simulation facility were investigated by quartz crystal microbalance (QCM), scanning electron microscopy (SEM) and X-ray Diffraction (XRD). The experimental results show that the oxidation behaviour of silver foil exposed to AO exhibits two stages: forming a thick Ag2O film at first, then forming AgO in the upper layer of the oxide film by the reaction of Ag2O film with O. At the first stage, the oxide layer cracked and spalled due to the development of stresses, so that new silver surface exposed out, and the further fast oxidation happened.