The superconductivity has always been one of the important topics in condensed matter physics. Recently, the discovery of superconductivity in potassium-doped picene have opened the way to a new class of organic superconductor, and at the same time metal-doped aromatic hydrocarbons have attracted great interest of researchers in investigating their physical and chemical properties. In this paper, according to the plane wave and pseudopotential method in the framework of density functional theory, we systematically study the structural and electronic properties of the K/Ba-codoped phenanthrene, including the atomic structure, band structure, density of states, formation energy, and charge transfer between dopant and phenanthrene molecule, and three meaningful conclusions have been drawn as follows. At first, the van der Waals interaction is found to play an important role in determining the atomic structure of metal-doped molecular solid, so it is necessary to include the interactions in these calculations. Secondly, due to the similarity in ionic radius, the combination of K and Ba is the favorable scheme for multiple-metal codoped phenanthrene crystal compared with K/Ca and K/Sr codoping schemes. From the viewpoint of formation energy, K1Ba1-phenanthrene has a bigger formation energy (-0.25 eV) per doped metal atom than K1Sr1-phenanthrene (-0.13 eV) and K1Ca1-phenanthrene (-0.04 eV). Thirdly, in order to realize the -3 valent state of phenanthrene molecule in K/Ba-codoped phenanthrene, the codoping of monovalent and bivalent metals is the only viable option due to the narrow interstitial space in molecular crystal. The bands crossing the Fermi level are from the lowest unoccupied molecular orbital (LUMO) and LUMO+1 orbital, resulting in the metallic state of K1Ba1-phenanthrene. The large density of states at the Fermi level is 17.3 eV-1, and these electronic states are mainly from C 2p orbitals and a little contribution from Ba 5d orbitals. Our studies present the electronic structure of K1Ba1-phenanthrene and suggest that K/Ba-codoping is a rational scheme to synthesize the superconductive sample, which provides a new route to the exploration of the promising superconductivity in metal-doped aromatic hydrocarbons.