Abstract: The optimized construction of co-catalysts holds great promise in promoting photocatalytic hydrogen production, offering significant value in understanding the mechanisms of photogenerated carrier separation and transport, as well as the distribution of active sites. In this study, a Ni-BP/CdLa₂S₄ (Black Phosphorus: BP) composite photocatalyst was in-situ constructed through ultrasonic exfoliation and a facile hydrothermal method. This composition exhibits broad-spectrum light absorption characteristics and excellent photocatalytic activity. The in-situ prepared Ni-BP-based nanosheet composite structure, endowed with photothermal properties, not only releases heat to enhance the mobility of photogenerated carriers but also serves as a hydrogen production co-catalyst to accumulate electrons and increase the active sites for catalytic reduction. Moreover, the formation of Ni—P bonds at the edges effectively enhances the stability of BP. The results show that the maximum hydrogen production rate of Ni-BP/CdLa₂S₄ reaches 24.7 mmol·g⁻¹·h⁻¹, which is 274 times that of pure CdLa₂S₄. Its excellent performance stems from the enhancement of light absorption capacity, the improvement of charge carrier separation, and the synergistic effect of photothermal response. This research provides new insights for constructing highly efficient and broad-spectrum active photocatalysts.