Herein, a unique 0D/2D nanodiamonds (NDs)/hematite (Fe2O3) composite photocatalyst was constructed by the solvothermal method and then was used to remove tetracycline pollutants in the aqueous solution, where the NDs nanoparticles were tightly anchored on the surface of hexagonal Fe2O3 nanosheets. The superior photocatalytic performance (85%, 180 min) was obtained by the optimum 15-NDs/Fe2O3 composite sample (containing 15 wt% NDs), which is approximately 4.13 times higher than that of pure Fe2O3. This is because the introduction of NDs nanoparticles not only promotes the visible-light absorption of Fe2O3, but also facilitates the separation of photogenerated electrons and holes in the interface of composite by the design of Z-scheme heterostructure. Besides, the intermediates, active species and reaction mechanism in the photocatalytic process were also discussed. This work enriches the knowledge in designing of novel 0D/2D Z-scheme heterojunction composites for photocatalysis.