Abstract: The low comprehensive energy storage performance, such as the charging energy density, discharging energy density, and energy storage efficiency, is a key scientific problem to be solved urgently in the energy storage ceramics field. Both improving the polarization difference (∆P) and breakdown field strength (BDS) of the ceramics are the key to enhance their comprehensive energy storage performance. With the main crystal phase BaTiO₃ (BT), utilizing the K_0.5Na_0.5NbO₃ (KNN) as the coating agent, sintering aid and additives, the BT-KNN ceramics with the grain sizes of 100 nm and 200 nm was synthesized, respectively. The BT-KNN ceramics has obvious nanodomains, relaxation behaviors and dielectric temperature stability, and with a high ∆P and high BDS. Compared with the BT-KNN ceramics with the grain size of 100 nm, the BT-KNN ceramics with the grain size of 200 nm has a better comprehensive energy storage properties, including high charging energy density W (2.50 J·cm⁻³), recoverable energy density W_rec (2.08 J·cm⁻³) and energy storage efficiency η (83.2%). This research may provide a theoretical basis for preparing high comprehensive energy storage performance ceramics.