This study aimed to prepare and apply a novel Pt/CdMoO₄ composite photocatalyst for photocatalytic N₂ fixation and tetracycline degradation. The Pt/CdMoO₄ composite was subjected to comprehensive investigation on the morphology, structure, optical properties, and photoelectric chemical properties. The results demonstrate the dispersion of Pt nanoparticles on the CdMoO₄ surface. Close contact between CdMoO₄ and Pt was observed, resulting in the formation of a heterojunction structure at their contact region. Density functional theory calculation and Mott-Schottky analysis revealed that Pt possesses a higher work function value than CdMoO₄, resulting in electron drift from CdMoO₄ to Pt and the formation of a Schottky barrier. The presence of this barrier increases the separation efficiency of electron-hole pairs, thereby improving the performance of the Pt/CdMoO₄ composite in photocatalysis. When exposed to simulated sunlight, the optimal Pt/CdMoO₄ catalyst displayed a photocatalytic nitrogen fixation rate of 443.7 μmol·L^‒1·g^‒1·h^‒1, which is 3.2 times higher than that of pure CdMoO₄. In addition, the composite also exhibited excellent performance in tetracycline degradation, with hole and superoxide species identified as the primary reactive species. These findings offer practical insights into designing and synthesizing efficient photocatalysts for photocatalytic nitrogen fixation and antibiotics removal.