We proposed a model to study the resistance degradation behavior of ferroelectric oxides in the presence of ferroelectric spontaneous polarization by combining the phase-field model of ferroelectric domains and nonlinear diffusion equations for ionic/electronic transport. We took into account the nonperiodic boundary conditions for solving the electrochemical transport equations and Ginzburg-Landau equations using the Chebyshev collocation algorithm. We considered a single domain structure relative to a thin film BaTiO3 single crystal orientated to the normal of the electrode plates (Ni) in a single parallel plate capacitor configuration. The capacitor was subjected to a dc bias of 0.5V either along the polarization direction or opposite to the polarization direction at 25 degrees C. It is shown that the polarization bound charges at the metal/ferroelectric interface play an important role in charge carrier transport and leakage current evolution in BaTiO3 capacitor.