Sodium niobate(NaNbO3)-based lead-free ceramics have attracted much attention in the pulse power capacitors due to their non-toxicity and superior energy storage properties. However, the large recoverable energy-storage density (Wrec) and efficiency (η) cannot be achieved simultaneously, thus restricting their commercialization. This work proposed astrategy of increasing the relaxation characteristics to improve the energy storage performance via constructing a local random field. The (1-x)(0.96NaNbO3- 0.04CaZrO3)-xBi0.5Na0.5TiO3 (x=0.05, 0.10, 0.15, and 0.20) antiferroelectric energy storage ceramics were prepared by a conventional solid-state method. The effect of Bi0.5Na0.5TiO3 content on the phase structure, microstructure and dielectric, ferroelectric as well as energy storage properties of 0.96NaNbO3-0.04CaZrO3 ceramics was investigated. The results show that the microstructure of each ceramic is homogeneous and dense. The (1-x)(0.96NaNbO3-0.04CaZrO3)-xBi0.5Na0.5TiO3 solid solution transformsfrom antiferroelectric orthorhombic P phase (x≤0.10) to antiferroelectric orthorhombic R phase (x≥0.15), accompanied by abroadening dielectric peak moving towards the lower temperatures as Bi0.5Na0.5TiO3 content increases, thus having the representative relaxation characteristics. The 0.85(0.96NaNbO3-0.04CaZrO3)-0.15Bi0.5Na0.5TiO3 ceramic has a maximum energy storage density Wrec of 1.614 J/cm3 and a high energy storage efficiency η of 83.97% under 260 kV/cm at room temperature. Besides, the ceramic exhibits a good temperature stability at 25-150 ℃ (the variation of Wrec less than 15%) and a high energy storage efficiency, which can be used as a promising material for high-temperature pulsed power capacitors.