Display omitted It is difficult for controlling the micro/nanostructures of composite unit on the surface of two-dimensional (2D) materials to fabricate the new high-efficiency photocatalysts. The mes-Fe3O4/g-C3N4 composite is fabricated by the modification of mesoporous Fe3O4 (mes-Fe3O4) nanospheres on the surface of 2D graphitic carbon nitride (g-C3N4) nanosheets. The mes-Fe3O4 nanospheres as the natural nanoreactors enlarge the specific surface area to increase reaction active sites, as well as provide the confined space to accelerate degradation reaction. Meanwhile, the physical and photoelectrochemical properties of mes-Fe3O4/g-C3N4 composite are distinctly improved owing to the electron collection effect of mes-Fe3O4 nanoreactors. The mes-Fe3O4/g-C3N4 composites exhibit the improved degradation performance for removing tetracycline hydrochloride (TC-HCl) relative to single g-C3N4. Moreover, the possible intermediate product and photocatalytic reaction mechanism are revealed in depth. This work gives a new guidance for the controlled fabrication of mesoporous nanoreactors on the surface of 2D materials.