The increase in energy consumption and its collateral damage on the environment has encouraged the development of environment-friendly ceramic materials with good energy storage properties. In this work, (1–x)Na_0.5Bi_0.5TiO₃-xCa(Mg_1/3Nb_2/3)O₃ ceramics were synthesized by the solid-state reaction method. The 0.88Na_0.5Bi_0.5TiO₃-0.12Ca(Mg_1/3Nb_2/3)O₃ ceramic exhibited a high recoverable energy storage density of 8.1 J/cm³ and energy storage efficiency of 82.4% at 550 kV/cm. The introduction of Ca(Mg_1/3Nb_2/3)O₃ reduced the grain size and increased the band gap, thereby enhancing the breakdown field strength of the ceramic materials. The method also resulted in good temperature stability (20–140 ℃), frequency stability (1–200 Hz), and fatigue stability over 10⁶ cycles. In addition, an ultrahigh power density of 187 MW/cm³ and a fast charge-discharge rate (t_0.9 = 57.2 ns) can be obtained simultaneously. Finite element method analysis revealed that the decrease of grain size was beneficial to the increase of breakdown field strength. Therefore, the 0.88Na_0.5Bi_0.5TiO₃-0.12Ca(Mg_1/3Nb_2/3)O₃ ceramics resulted in high energy storage properties with good stability and were promising environment-friendly materials for advanced pulsed power systems applications.