Ordered domain engineering has been further developed for modifying and improving physical properties in complex perovskite ceramics. In the present work, Ba(Ni_1/3Nb_2/3)O₃ ceramic is taken as a typical example for ordered domain engineering, in which the sintering temperature lies above the order-disorder transition temperature. Though the well-ordered structure could not be obtained in as-sintered samples, high ordering degree could be achieved together with preferred ordered domain structures in Ba(Ni_1/3Nb_2/3)O₃ ceramics through long-time annealing, and subsequently the physical properties such as electrical resistivity, thermal conductivity, dielectric strength and energy storage density are significantly enhanced, where the ordering degree, ordered domain structure and ordered domain boundary play the critical rules. The present work provides an effective approach for developing complex perovskite dielectric ceramics with superior physical properties.