It's highly desired to design and fabricate an effective Z-scheme photo-catalyst with excellent charge transfer and separation, and a more negative conduction band edge (E_CB) than O₂/·O₂⁻ (−0.33 eV) and a more positive valence band edge (E_VB) than ·OH/OH⁻ (+2.27 eV) which provides high-energy redox radicals. Herein, we firstly designed and synthesized a core–shell-heterojunction-structured Z-scheme system BaTiO₃@In₂S₃ (BT@IS, labelled as BTIS) through a hydrothermal method, where commercial BT was used as the core and In(NO₃)₃·xH₂O together with thioacetamide as the precursor of IS was utilized as the shell material. In this system, the shell IS possesses a E_CB of −0.76 eV and visible-light-response E_g of 1.92 eV, while the core BT possesses a E_VB of 3.38 eV, which is well suited for a Z-scheme. It was found that the as-prepared BTIS possesses a higher photocatalytic degradation ability for methyl orange (MO) than commercial BT and the as-prepared IS fabricated by the same processing parameters as those of BTIS. Holes (h⁺) and superoxide radicals (·O₂⁻) were found to be the dominant active species for BTIS. In this work, the core–shell structure has inhibited the production of ·OH because the shell IS has shielded the OH⁻ from h⁺. It is assumed that if the structure of BTIS is a composite, not a core–shell structure, ·OH could be produced during photocatalysis, and therefore a higher photocatalytic efficiency would be obtained. This current work opens a new pathway for designing Z-scheme photocatalysts and offers new insight into the Z-scheme mechanism for applications in the field of photocatalysis.