We use the MPB4 theory to calculate the differential capacitance of the interface between NaBr + water and tetrabutylammoniumtetraphenyl borate (TBATPB) + nitrobenzene at electrolyte concentrations of 0.01 M, 0.02 M and 0.05 M. In addition to the effects of ion size and image force, we consider the influence of the electrolyte concentration, the surface charge density and the solvent effect on the potential distribution of the inner layer. The influence can be ascribed to ionic penetration into the opposite solution and ion-ion correlations across the interface. Our results are in better agreement with the experimental values than are other theoretical values. We conclude that the MPB4 theory-describes the structure of the water nitrobenzene interface well provided that the influence of the electrolyte concentration, the surface charge density and the solvent effect on the inner-layer potential distribution are included in the calculation.