A theoretical investigation was carried out to study the electronic and geometric structure of a conjugated poly-phenyl-based molecular resonant tunneling diode, which was  experimentally demonstrated to behave like a molecular resonant tunneling diode. The molecule under investigation consists of three phenyl rings connected via two acetylene functional groups, where two H atoms of the middle phenyl ring were replaced by –NH₂ and –NO₂ groups. The electron transport behavior through this molecule was interpreted from the spatial orientation of the lowest unoccupied molecular orbitals, which extend across the molecule.The result indicates that approximately 2.2 eV bias voltage is required for the electronic transport to be observed,which is in good agreement with experimental results.