To clarify the electron transfer behavior of the hydrogen-terminated boron-doped diamond film electrode in an electrolytic solution, its detailed electronic structures were investigated by using scanning probe microscopy and ab initio methods. The interface structure of the hydrogen-terminated diamond electrode and the electrolyte was also studied by means of cyclic voltammetry and AC impedance spectroscopy. The results showed that there exist shallow acceptors in the band gap of the hydrogenated diamond films. Neither the surface hydrogen alone nor the subsurface hydrogen could induce the shallow acceptors, though they interact strongly with the surface carbon atoms or subsurface carbon and boron atoms in the diamond film. It is the interaction of the surface adsorbates and the surface C-H bonding that gives rise to the shallow acceptors in the band gap of the hydrogenated diamond film. The surface shallow acceptors in the band gap of the hydrogenated diamond film could lower the energy barrier of the electron transfer between the diamond electrode and the electrolytic solution. Thus, electrochemical window for the hydrogenated diamond film is narrower and, its film resistance and capacitance are also smaller than those of the oxygenated one. In our work, the experimental data obtained by using scanning probe microscopy are in good agreement with the calculation results. (C) 2009 Elsevier B.V. All rights reserved.