In this paper, the Bi2WO6 quantum dots (QDs) decorated g-C3N4 nanoplates were successfully synthesized via a one-step hydrothermal method. The morphology of the Bi2WO6 could be tuned from regular nanoplates to quantum dots. Remarkably, the Bi2WO6 QDs coupled with g-C3N4 not only prevented the aggregation, but also decreased the size of Bi2WO6 QDs about 3.5 nm. Meanwhile, the charge separation mechanisms of Bi2WO6 QDs/g-C3N4 photocatalyst were investigated by electrochemical impedance spectra, Mott-Schottky and linear voltammetry scans. As a result, the photoelectrochemical (PEC) experiments provided forceful evidence for the charge separation mechanism of the Bi2WO6 QDs/g-C3N4 Z-scheme. The Z-scheme system not only accelerated the separation efficiency of charge, but also improved the ability of PEC water splitting at measured 1.23 V vs. RHE. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.