In this study, Ca1-xSrxCu3Ti4O12/TiO2 ceramics doped with different Sr/Ca ratios and an excess of 20% nano-scale TiO2 particles were prepared via the solid-state method (denoted as C1-xSxCTO/TiO2, where x = 0, 0.2, 0.4, 0.6, 0.8, 1.0). The phase composition, microstructure, elemental distribution, elemental valence states, and electrical properties of the composite ceramics were systematically analyzed. XRD data confirmed the successful synthesis of CSCTO crystals in a series of CSCTO ceramics, and it was observed that the lattice parameters of the main phase increased as the Sr/Ca ratio in CSCTO/TiO2 increased. Ca0.8Sr0.2Cu3Ti4O12/TiO2 ceramics demonstrated a good dielectric constants (1 × 105, 1 kHz) at room temperature. Microstructure analysis revealed that the excess TiO2 hinders the composite ceramics' crystal growth, forming pomegranate-like structures. The structure leads to a hierarchical interfacial polarization, which results in the giant dielectric response in CSCTO/TiO2 composite ceramics.