In this paper, 0.7(Na0.5Bi0.5)TiO3-0.3(Sr0.7Bi0.2)TiO3-xZnNb2O6 (abbreviated as BNT-SBT-xZN, where x=0.5%, 1.0%, 1.5% and 2.0%, molar fraction) ceramics were prepared by the solid-state reaction method. The effect of ZnNb2O6 doping on the structure and properties of BNT-based ceramic materials was studied. The results show that, BNT-SBT-xZN ceramics doped with a small amount of ZnNb2O6 (x=0.5%) have pure perovskite structure with compact microstructure and no second phase. At room temperature, they are typical relaxor ferroelectrics (dispersion index γ>1.7). For all unpoled and poled BNT-SBT-xZN ceramics of x=0.5%, the transition temperature of ferroelectric-relaxation (TR-E) is lower than room temperature, while TR-E is below 100 ℃, which denotes the dielectric anomalous associated with thermal relaxation of polar nano regions (PNRs) in rhombohedral (R3c) and tetragonal (P4bm) symmetrical structure. When the content of ZnNb2O6 increases, the ergodic relaxor state gradually plays a dominant role, maximum polarization (Pmax) and remanent polarization (Pr) both show a decreasing trend. BNT-SBT-xZN ceramics with x=0.5% have high Pmax, low Pr and large ΔP, resulting in excellent energy storage characteristics and frequency and temperature stability with Pmax of 44.7 μC/cm2, Pr of 12.4 μC/cm2, ΔP of 32.3 μC/cm2, energy density (W1)of 1.066 J/cm3, energy storage efficiency (η) of 48.68% under 110 kV/cm. Moreover, discharge energy density Wd, maximum discharge current Imax, current density CD and power density PD of 0.60 J/cm3, 45.33 A, 1 443 A/cm2 and 72.2 MW/cm3 are obtained at room temperature and 100 kV/cm, respectively.