Abstract: In frame of the scattering-matrix theory and Fermi-Thomas
approximation, we had investigated the conductance properties of
mesoscopic structure in dc case by employing a quantum tunneling
structure with single barrier. Results clearly indicate that, the
contact effect has notable affection on the transmission probability
of electrons and the distribution of internal potential in
mesoscopic system; even though dc case, the behaviors of conductance
displayed in potential drop conflict with the Kirchhoff's laws in
classical circuit, and the total resistance of the mesoscopic system
cannot be expressed as contact resistance in series with 'scatterer'
resistance. So the quantum coherence between contacts and devices is
worth considering, the role of contacts effect is important for
further investigation of the electron transport in mesoscopic
system.

Key words: electron transport, mesoscopic system, scattering-matrix theory, Fermi-Thomas approximation