Polarization response and thermally stimulated depolarization current (TSDC) of BaTiO3-based ceramic multilayer capacitors with Y5V specification were studied. The temperature dependence of dielectric behavior shows that as the dc electric field increases, the polarization response in the whole measurement range (from -125 degrees C to +350 degrees C) is suppressed. As the temperature rises to about 250 degrees C, dielectric loss significantly increases and has a dependence on dc electric field, due to the leakage behavior at high temperature. According to the hysteresis loops, the calculated electrostatic energy density and energy efficiency are also closely related to polarization-electric field. Utilizing a fixed measuring polarization condition, two TSDC relaxation peaks are observed and both are associated with oxygen vacancies. It is demonstrated that the weak peak originates from the in-grain migration of oxygen vacancies and the strong peak with high relaxation temperature is caused by the across grain-boundary oxygen vacancies. The activation energy estimated for the relaxation of oxygen vacancies across grain boundaries is about 0.78eV. The main contribution for the leakage behavior is from the across grain-boundary relaxation of oxygen vacancies. With increasing of temperature and electric field stress, the extrinsic oxygen vacancy defects show more fluent migration, which eventually leads to the resistance degradation and breakdown.