<p>This paper employs first-principles calculations to investigate the structural electronic and optical property variation mechanisms of A-site composite element doped BaTiO₃ ceramics BaBi<i>X</i>TiO₃ (<i>X</i> = Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ra²⁺). Through calculations of the systems’ band structures density of states dielectric functions reflectivity refractive indices optical absorption coefficients and extinction coefficients, it is found that A-site Be²⁺ doping achieves high static permittivity (<i>ε</i>₀ = 146.77) in the low-energy region through lattice distortion and oxygen vacancy compensation demonstrating potential in metamaterial design; Mg²⁺ exhibits extreme ultraviolet (EUV) response (<i>ε</i>₂ = 17.05) suitable for EUV detectors; the low-loss characteristics and structural stability of Ca²⁺/Sr²⁺ provide theoretical foundations for high-frequency filters. This study reveals the critical roles of doping element ionic radii valence states and orbital hybridization in multiband optical responses providing theoretical guidance for designing high-voltage capacitors photocatalytic materials and nuclear radiation shielding devices.</p>