In this study, Cu-doped Zn-In-S/ZnS core/shell quantum dot (QD) white-light-emitting diodes (WLEDs) are prepared, and the influence of the shell thickness on their properties is investigated. With several groups of QD WLEDs, the QD ratio of green and orange light is different to measure the properties of the International Commission on illumination (CIE) color coordinates, color rendering index (CRI), correlated color temperature (CCT), and luminous efficiency (LE). It is found that the LE and CRI of thick Cu‍‍∶‍Zn-In-S/ZnS core/shell QD WLEDs are higher than those of the thin Cu‍∶‍Zn-In-S/ZnS core/shell QD WLEDs. Additionally, when the thickness of the shell increases, the stability of QDs is enhanced and the luminous efficiency is increased.