The influences of electron and phonon confinement and interface effects on the thermoelectric performance of SrTiO3 nano-ceramic are studied by using the Boltzmann transport equations and density functional calculations. Theoretical calculations show that the figure of merit of nano-ceramic is greatly improved up to 0.8 at room temperature. The improvement is due mainly to the phonon confinement effect and the electronic energy filtering effect at the grain boundary. The electron confinement effect and the interface phonon scattering effect play a supporting role. These results may be conducive to the design of high-performance thermoelectric nano-ceramic.