The adsorption of O and H atoms on the Fe3O4(111) surface was investigated using ultraviolet photoemission spectroscopy (UPS) and first-principles calculations. On the FeA1-terminated surface, H adsorption decreases the work function without changing the density of states near the Fermi level. The density of states near the Fermi level decreases by O adsorption. On the O/FeA1-terminated surface, H adsorption dramatically increases the density of states near the Fermi level, indicating that the Fe 3d state is modified. The first-principles calculations showed that the electronic structure of the surface FeA on the FeA1-terminated surface is half metallic with its spin up forming an isolated spin-polarized conductive layer. By O adsorption, the up-spin band at the Fermi level of the surface FeA site is removed, and the Fermi level of the surface FeA moves to the down-spin t(2g) band. By subsequent H adsorption, electrons are doped to the FeA1 site, and the surface FeA1 layer becomes semiconducting. These results indicate that the charge and spin structure is modulated by O and H adsorption.