Abstract: Photocatalytic ammonia (NH₃) decomposition is a key strategy for green hydrogen production and renewable energy conversion. Although conventional plasmonic metal/TiO₂ composites exhibit some activity, their applications are constrained by high carrier recombination rates and narrow light harvesting ranges. To address these challenges, this study innovatively introduces the plasmonic semiconductor MoO_3–x, which is characterized by broad-spectrum absorption and abundant oxygen vacancies, to construct a Cu-MoO_3–x/TiO₂ plasmon resonance coupling nanostructure. The construction of the Cu-MoO_3–x composite stabilizes Cu via MoO_3–x coating and facilitates electron transfer from Cu to MoO_3–x, generating more oxygen vacancies for NH₃ activation. The visible localized surface plasmon resonance (LSPR) response of Cu, coupled with the visible to near-infrared LSPR resonance of MoO_3–x, broadens the spectral response and optimizes carrier dynamics, thereby reducing the recombination of photogenerated carriers. The use of hot carriers and plasmonic photothermal effects synergistically accelerate surface reaction kinetics and enhance photocatalytic efficiency. In particular, the optimal Cu-MoO_3–x/TiO₂ catalyst results in an enhanced NH₃ decomposition rate of 103.2 mmol·g^–1·h^–1 under full-spectrum light irradiation, representing 29-fold and 94-fold enhancements over those of Cu/TiO₂ and MoO_3–x/TiO₂, respectively. This innovative design strategy transcends traditional plasmonic metal/semiconductor catalyst designs and opens new avenues for developing efficient solar-driven plasmon resonance coupling catalysts.