Under the tight-binding approximation, the geometric structure of the Zn/GaAs(110) surface is calculated by a self-consistent total energy method. It is found that the surface relaxation structure is a universal characteristic for low coverage adsorption, which is important in determining the Fermi level. The bonding states are pinned at 0.73eV above the top of the valence band by the covalent hybridization of the highly localized Zn s orbitals and the surface Ga sp３ dangling bonds. A comparison is made with theoretical and experimental results of free and other adsorbate GaAs(110) surfaces.