The utilization of visible light for photocatalytic nitrogen fixation offers a sustainable and eco-friendly strategy for the production of ammonia. The present study focuses on the synthesis of a series of rare earth-doped carbon nitride composite ultraviolet-activated Ce-UiO-66 catalysts, denoted as RECN-actMOF, for efficient nitrogen fixation. Rare earth doping modulates the band structure of carbon nitride, facilitating the formation of a type-I heterojunction with Ce-UiO-66 and promoting photocarrier generation at nitrogen fixation sites. Among these, Sm-doped SmCN-actMOF exhibits high visible-light absorption and efficient utilization of photocarriers, resulting in an apparent quantum efficiency (AQE) of 1.58% under 495 nm light irradiation. This study provides a pathway for enhancing the nitrogen fixation efficiency of photocatalysts through the incorporation of rare earth elements, and expanding the potential applications of rare earth materials in the field of photocatalysis.