Sluggish hole transfer and the resulting pronounced charge recombination hinder the efficiency of photocatalytic overall water splitting. Herein, we present Si quantum dots (SiQDs) as hole transporter to construct SiQDs/Cu-doped ZnIn2S4 heterojunction photocatalysts (Cu0.48SZ) for overall water splitting. Under visible light illumination, Cu0.48SZ exhibits highly stable overall water-splitting activity of 210 μmol g−1 h−1 H2 and 97 μmol g−1 h−1 O2 with an apparent quantum yield (AQY) of 2.57 % at 420 nm. Results demonstrate that the synergy of SiQDs and Cu doping enhances carrier-separation efficiency and reduce surface kinetic barriers, leading to high photocatalytic performance. The presence of SiQDs effectively accelerates the transfer of photoexcited holes and avoids the self-oxidation of ZnIn2S4, favoring water oxidation. The Cu doping increases the electron density around the S atoms of ZnIn2S4 and thus promotes water reduction. This work extends the application of SiQDS as efficient hole transporter for photocatalytic overall water splitting.