The properties of co-adsorption of K with O on the Ag(ll0) surface have been investigated with X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), electron energy loss spectroscopy (EELS) and low energy electron diffraction (LEED). It is shown that, at low potassium coverages, there are two distinct oxygen species on the Ag(ll0) which are determined as the dissolved and chemisorbed atomic oxygen species. With K coverage increasing, the molecular oxygen is developed, which is associated with subsurface K. These oxygen species peaks can be clearly distinguished from UPS as well as XPS. The initial sticking coefficient of the K precovered Ag surface for oxygen adsorption is enhanced. K and O display a mutual enhancement of surface to bulk transport. A monolayer K atoms forms (1×2) LEED pattern on the Ag(ll0) surface, which is consistent with the early results. The surface structure, however, transfers into a (2×1) ordered structure when oxygen is exposed to the surface. A mode] for co-adsorption of K with O on the Ag(ll0) is proposed.