Abstract: K_0.5Na_0.5NbO₃(KNN) ceramics exhibit low room-temperature permittivity, large remanent polarization and low breakdown electric field, which resulting in poor energy storage performance. Herein, the K_0.495Na_0.495Tm_0.003La_xBi_(0.007−x)Nb_0.7Ta_0.3O₃(x=0.05%-0.2%) ceramics were fabricated via an A/B-site co-doping strategy: the refined ceramic grains, along with cation vacancies and oxygen vacancies induced by donor doping of A-site Bi³⁺、La³⁺ and Tm³⁺, lead to an increased dielectric constant; Dopants with distinct ionic radii and valence states facilitate the formation of polar nanoregions (PNRs), which reduced the remanent polarization P_r. Grain refinement coupled with bandgap widening originating from A/B-site La³⁺ and Ta⁵⁺ raised the breakdown electric field E_b. The K_0.495Na_0.495Tm_0.003La_0.001Bi_0.006Nb_0.7Ta_0.3O₃ ceramic exhibited optimal excellent dielectric and energy storage performance: room-temperature permittivity ε_r=1646 at 100 kHz, tanδ=0.036, relaxation factor γ=1.81, low P_r of 1.5 μC/cm² and enhanced E_b of 130 kV/cm, an energy storage density of 1.22 J/cm³ and efficiency of 86% are obtained. The simultaneous enhancement of dielectric and energy-storage performances make KNN-based ceramics have certain application potential in the fields of pulse power capacitors and energy storage.