Abstract: Based on the first principles,the electrical properties of a molecular wire consisting of aromatic hydrocarbon and gold surface was investigated.Density functional theory is employed to obtain the electronicstructures of the molecule and the extended molecule.Then the interaction energy and the transmission spectra between the molecule and the gold surface were determined quantitatively.The elastic Green function method is applied to study its current-voltage properties.Numerical results show that the energy gap between HOMO and LUMO,theπelectron number,the interaction energy between the molecule and the gold surface and the molecule orbital expansibility have great effect on the electrical properties of molecular wires.