Lead-free bulk ceramics for advanced pulsed power capacitors show relatively low recoverable energy storage density (Wrec) especially at low electric field condition. To address this challenge, we proposed an A-site defect engineering to optimize the electric polarization behavior by disrupting the orderly arrangement of A-site ions, in which Ba0.105Na0.325Sr0.245−1.5xð0.5xBi0.325+xTiO3 (BNS0.245−1.5xð0.5xB0.325+xT, x = 0, 0.02, 0.04, 0.06, 0.08) lead-free ceramics were selected as the representative. The BNS0.245−1.5xð0.5xB0.325+xT ceramics were prepared by using pressureless solid state sintering and achieved large Wrec (1.8 J/cm3) at a low electric field (@110 kV/cm) when x = 0.06. The value of 1.8 J/cm3 is super high as compared to all other Wrec in lead-free bulk ceramics under a relatively low electric field (< 160 kV/cm). Furthermore, a high dielectric constant of 2930 ± 15% in a wide temperature range of 40 ~ 350°C was also obtained in BNS0.245−1.5xð0.5xB0.325+xT (x = 0.06) ceramics. The excellent performances can be attributed to the A-site defect engineering, which can reduce Pr and improve the thermal evolution of polar nanoregions (PNRs). This work confirms that the BNS0.245−1.5xð0.5xB0.325+xT (x = 0.06) ceramics are desirable for advanced pulsed power capacitors, and will push the development of a series of BNT-based ceramics with high Wrec and high temperature stability.