The geometric, electronic and magnetic properties of a nitric oxide (NO) adsorbed Fe3O4(100) surface have been investigated using density functional theory (DFT) calculations. NO molecules preferentially bond with surface Fe(B) atoms via their N atoms. The generalized gradient approximation (GGA) is not recommended to be used in such a strongly correlated system since it provides not only an overestimation of the adsorption energy and an underestimation of the Fe(B)-N bond length, but also magnetic quenching of the adsorbate and the bonded Fe(B) atoms. In contrast, a tilted geometry and magnetization of the adsorbate and the bonded Fe(B) atom are obtained after including the strong on-site Coulomb interactions through a Hubbard term (GGA+U). The spin-down 2π* states of the NO molecule are filled and broadened due to the adsorbate-substrate interaction and the molecule-molecule interaction. The surface spin polarization close to the Fermi level is expected to be greatly enhanced by the NO adsorption which has significance for interface design in spintronic devices.