After bombarding the Ni(001) surface by an Ar ion beam with primary energy of 500 eV and beam current of 5 μA in the presence of residual nitrogen under a total pressure of 5×10-5 torr, we have found a P(2×2) structure formed by the adsorption of nitrogen on Ni(001) surface by means of LBED. This is much similar to the structure caused by the adsorption of oxygen or the segregation of carbon with a surface concentration of one quarter monolayer on the same crystal surface. A primary discussion on the nature of nickel-nitrogen bond has been made.