The open-air fabrication of quantum-dot light-emitting diodes (QLEDs) shows great potential for scalable manufacturing. However, the processing stability of QLED devices remains a fundamental barrier to their industrialization. This study investigates the gas-related stability of QLEDs based on the ZnMgO electron transport layer (ETL). By analyzing the current density–voltage (J–V) characteristics of QLEDs and the corresponding sub-devices of functional layers in different gas environments, we demonstrate that the ZnMgO ETL plays a critical role in determining the gas-related stability of QLEDs. Further characterizations and density functional theory (DFT) calculations indicate that gas-induced surface reactions—particularly modifications to surface states and the formation of stable ZnMgO/OH—are the primary causes of performance degradation of QLEDs.