<p>Currently, based on the unique spatial structure and properties of three-dimensional ordered macroporous (3DOM) materials, the photocatalytic performance of composites can be effectively enhanced by loading semiconductors with photocatalytic activity on the surface and designing and constructing heterostructures. In this study, polystyrene (PS) microspheres were prepared using the self-assembly technology. In₂S₃@3DOM NiTiO₃-TiO₂ composite was then fabricated via a vacuum impregnation and constant-temperature water bath method, of which the crystal phase and microstructure analysis revealed that In₂S₃@3DOM NiTiO₃-TiO₂ exhibited a well-defined crystal structure and 3DOM morphology. This 3DOM structure provided more reactive sites with a substantial mass transfer capacity, and its slow photon effect could enhance the light absorption. Photoluminescence and photoelectrochemical tests demonstrated that the heterojunction interfaces among In₂S₃, NiTiO₃, and TiO₂ in In₂S₃@3DOM NiTiO₃-TiO₂ effectively promoted the separation of electron–hole pairs and significantly extended the carrier lifetime. Under simulated sunlight conditions, the removal rate of crystal violet (CV) as the target pollutant by In₂S₃@3DOM NiTiO₃-TiO₂ achieved 99.98%. Moreover, with Pt as the cocatalyst, its photocatalytic hydrogen production performance was 12 times higher than of commercial TiO₂. Through active species capture experiments, Mott–Schottky tests, and UV–vis diffuse reflectance tests, the photocatalytic reaction mechanism of the double Z-scheme heterostructure among In₂S₃, NiTiO₃, and TiO₂ was speculated, and the possible photocatalytic degradation pathways were analyzed. The double Z-scheme heterostructure regulated the charge transfer path. It enhanced the separation efficiency of electrons and holes, and the 3DOM slow photon effect strengthened the light capture ability of the composite material, further significantly improving its photocatalytic performance.</p>