High-performance dielectric capacitors are one of the key components of pulsed power systems. Recently, with the rapid development of new energy sources, achieving a large energy storage density and a high efficiency in relaxor ferroelectric ceramics becomes the focus of our research. However, owing to the low breakdown strength (Eb), it is still a challenge to achieve high recoverable energy storage density (Wrec) in (Bi0.5Na0.5)0.7Sr0.3TiO3-based ceramics. The doping of Sm(Mg0.5Zr0.5)O3 can effectively increase the activation energy of the ceramics and reduce the oxygen vacancy concentration. Therefore, a giant Wrec of ∼6.2 J/cm3 and a high energy storage efficiency (η) of ∼82.4 % are realized in 0.88(Bi0.5Na0.5)0.7Sr0.3TiO3-0.12Sm(Mg0.5Zr0.5)O3 ceramics at Eb = 455 kV/cm. Besides, the ceramic also possesses a high current density of 611.5 A/cm2, a high-power density of 55.0 MV/cm3 and the fast discharge rate near 10.0 ns. This strategy to improve the energy storage performance opens up a new and effective way for future research on lead-free energy storage ceramics. •The enhancement of Eb is realized in BNST ceramics.•Wrec of 6.2 J/cm3 and η of 82.5% are achieved in 0.12SMZ ceramic.•The 0.12SMZ ceramic exhibit excellent frequency and temperature stability.•High CD of 611.5 A/cm2 and PD of 55.0 MV/cm3 at an applied electric field of 180 kV/cm.