<p>K_xBi_(2−x)/3Cu₃Ti₄O₁₂ (0.05 ≤ x ≤ 0.20) ceramics were prepared using the traditional solid-state reaction method. Owing to the liquid-phase sintering mechanism, a high K⁺ doping concentration promotes the formation of a TiO₂–CuO eutectic liquid phase, resulting in considerable grain growth and enhanced grain connections. EDS and Mapping indicated that the components with larger grain sizes precipitated more CuO particles on the surface after polishing and annealing treatments. K_0.05Bi_1.95/3Cu₃Ti₄O₁₂ shows the highest dielectric constant (~ 2.1 × 10⁵) and a low dielectric loss (~ 0.21) at 1&#xa0;kHz. The complex impedance spectra revealed that the excellent dielectric properties of the ceramics originated from the response of the internal and surface barrier layer capacitors. The substantial precipitation of CuO results in a significant increase in the grain boundary resistance. The K_xBi_(2−x)/3Cu₃Ti₄O₁₂ ceramic element gradient distribution model was developed based on the X-ray photoelectron spectroscopy fitting analysis on the surface and within the ceramics. The Schottky width effect between the electrode and ceramic and internal microinterface structure on the dielectric properties were analysed in detail based on the proposed model.</p>