A high-entropy relaxor ferroelectric ceramic, (Sr₀.₂Ba₀.₂Pb₀.₂La₀.₂Na₀.₂)Nb₂O₆ (SBPLNN), was developed to achieve ultrahigh energy storage performance. This material, based on a tetragonal tungsten bronze (TTB) structure, utilizes an equimolar-ratio element design to enhance atomic-scale compositional heterogeneity, which modulates relaxor features and induces lattice distortion. This results in reduced polarization hysteresis and enhanced breakdown endurance. SBPLNN exhibits a recoverable energy density of 11.0 J·cm⁻³ and an energy efficiency of 81.9% under a high electric field of -753 kV·cm⁻¹. The material also demonstrates exceptional fatigue, temperature, and frequency stability, as well as superior charge-discharge performance. The high-entropy design enables the material to achieve a record-high energy storage capacity, surpassing previously reported dielectric ceramics. The study highlights the effectiveness of the equimolar-ratio high-entropy strategy in developing advanced dielectric materials with exceptional energy storage capabilities. The results demonstrate that SBPLNN ceramics have significant potential for practical applications as high-power pulse capacitors.A high-entropy relaxor ferroelectric ceramic, (Sr₀.₂Ba₀.₂Pb₀.₂La₀.₂Na₀.₂)Nb₂O₆ (SBPLNN), was developed to achieve ultrahigh energy storage performance. This material, based on a tetragonal tungsten bronze (TTB) structure, utilizes an equimolar-ratio element design to enhance atomic-scale compositional heterogeneity, which modulates relaxor features and induces lattice distortion. This results in reduced polarization hysteresis and enhanced breakdown endurance. SBPLNN exhibits a recoverable energy density of 11.0 J·cm⁻³ and an energy efficiency of 81.9% under a high electric field of -753 kV·cm⁻¹. The material also demonstrates exceptional fatigue, temperature, and frequency stability, as well as superior charge-discharge performance. The high-entropy design enables the material to achieve a record-high energy storage capacity, surpassing previously reported dielectric ceramics. The study highlights the effectiveness of the equimolar-ratio high-entropy strategy in developing advanced dielectric materials with exceptional energy storage capabilities. The results demonstrate that SBPLNN ceramics have significant potential for practical applications as high-power pulse capacitors.