Developing high water resistance, efficient, and stable, functional catalysts under practical working conditions is significant reducing and controlling VOCs (volatile organic compounds). It is a considerable challenge to elucidate the catalytic process and mechanism of VOCs degradation under the action of environmental water. In this study, CoCu-CeO₂ trimetallic oxide catalysts are designed to investigate the catalytic performance in the water-toluene complex system by modulating the morphological and structural characteristics of the bimetallic at the multiphase interface. The result indicates that introducing Cu species enhances the electron transfer process from Co³⁺ to Co²⁺resulting in improved redox performance. Co species significantly promote the migration and conversion of the Cu species at the nanoscale to achieve lattice atom substitution. The bimetallic substitution enhances the ability of CeO₂ to form oxygen defects. In the presence of ambient water, Co-Cu interactions inhibit the oxidation of toluene to benzaldehyde and benzoic acid by-products with enhanced mineralization of toluene. Design defects and multi-metal sites play a crucial role in the O₂-H₂O-toluene reaction system. The construction of this catalyst system provides scientific guidance in efficiently removing volatile organic pollutants in complex multi-media environments.