Facet engineering has played a crucial role in influencing the fundamental properties of conventional semiconductor nanocrystals, including their surface structures and charge carrier dynamics. However, facet control in zero-dimensional colloidal CsPbBr₃ perovskite nanocrystals (PNCs) remains much less explored, primarily owing to the absence of precise synthetic methodologies. Typically, PNCs are predominantly enclosed by {100} facets under thermodynamic control. This work reports the synthesis of gradient-truncated CsPbBr₃ PNCs with exposed non-{100} facets, in which the truncation degree can be precisely modulated by introducing sulfide ions (S²⁻) as regulators. The added S²⁻ ions bind to surface Pb²⁺ sites in PNCs and suppress the closure of high-energy non-{100} facets during the synthesis, thereby regulating the exposure of these facets. These gradient-truncated products exhibit enhanced CO selectivity for photocatalytic CO₂ reduction, with the selectivity showing a positive correlation with truncation degree. The photocatalytic selectivity is attributed to the disparity in adsorption energies of reduction products on {110} facets and the enrichment of photogenerated electrons driven by facet polarity.