the development of X9R type (−55 to 200℃, ΔC/C_25℃≤ ±15%) high-performance ceramic dielectric materials has been accelerated by the advancement in high-capacity and high-temperature stability of Multilayer Ceramic Capacitors (MLCCs). In this study, the conventional solid-state reaction method was employed to systematically investigate the effects of the individual and synergistic doping of rare earth elements Dy and Ho on the phase structure, microstructure, and dielectric properties of 0.9BaTiO₃–0.1(Bi_0.5Na_0.5)TiO₃–0.02Nb₂O₅ ceramics. As a result, a wide-temperature stable X9R type BaTiO₃-based ceramic dielectric material was successfully prepared. The experimental results indicate that the ceramic grains of rare earth elements Dy and Ho exhibit a typical “core-shell” structure, demonstrating good temperature stability. The optimal dielectric performance is achieved at room temperature when Dy = 0.75 mol% and Ho = 0.25 mol% are synergistically doped, with the highest dielectric constant reaching 1725, and the temperature coefficient of capacitance (TCC, −55 ℃ ~200 ℃) ≤ 15%. The material 0.9BaTiO₃–0.1(Bi_0.5Na_0.5)TiO₃–0.02Nb₂O₅–0.75Dy₂O₃–0.25Ho₂O₃, with its high dielectric constant and excellent X9R type temperature characteristics, is a promising candidate for high-temperature MLCC applications.