The oxygen adsorption on Au (111) surface has been studied systematically using density function theory (DFT). The adsorption energies, adsorption structures, work functions, density of electrons and projected density of states have been calculated in wide ranges of coverage. It is found that the fcc-hollow site is the energetically favorable site for all the coverage range considered. The repulsive interaction has been identified, and the adsorption energy decreases with the coverage θ, while work function increases linearly with the coverage. It has been found that the O-Au interaction is very weak due to the fully occupied anti-bonding states from O 2p and Au 5d hybridization.