The adsorption of atomic oxygen on the Ni（111） surface has been systematically investigated through first-principles DFT-GGA methods in wide ranges of coverage. It was found that the fcc hollow site is the energetically most favorable for the whole coverage range considered. The adsorption energy decreases with the coverage θ，while the work function increases linearly with the coverage.It can be also concluded from analysis of the electron density and projected density of states that the electron transfer from the substrate （Ni atoms） to the O atom gives rise to the appearance of a dipole moment, which results in a large increase in the work function. The O—Ni interaction between Ni 3d and O 2p orbitals results in the formation of bonding and antibonding states, while the antibonding states are hardly occupied. Therefore, the bonding interaction between O and Ni is stonger, and the adsorption energy is larger.