In the study of Quantum-Dot Light-Emitting Diodes (QLEDs), theambient air, especially water and oxygen, has been a major factor affecting device performance. However, some phenomena have shown that water is one of the causes of the increase of luminance under the certain current of QLEDs. Therefore, this effect can be improved by water vapor treatment to optimize device performance greatly. This work aims to study the effect of water vapor treatment to the performance of Quantum-Dot Light-Emitting Diodes (QLED) based on the passivation of the surface states of the quantum dots by water and explore the best processing time. Firstly, The QLEDs were fabricated through solution processes, and after the fabrication of the emission layer, the QLEDs were placed in the argon atmosphere with a certain humility. In this progress, the degree of water vapor treatment was depended by the different processing time, and the effect of air was isolated by the argon atmosphere. Secondly, the electroluminescence spectra of each device were characterized. The results show that the spectrum of treated QLEDs has a slight blue shift and the shift increases with the increase processing time. The reason for the blue shift is that the particle sizes of QDs decrease due to the oxidation of the surface states of the quantum dots by water. In addition, the current density-voltage-luminance (J-V-L) curves were characterized. The luminance and current intensity of each device was compared, and the current efficiency-current intensity (CE-J) curves were obtained. The results show that the luminance and CE of QLEDs with water vapor treatment were greatly improved with the extension of the processing time. (The luminance is increased by 10%, and the CE is increased by 50% when the processing time is 3 mins) In the end, the luminance of all QLEDs in the certain current were tested and the luminance-time curves were obtained. The aging curves show that the luminance of each QLEDsincreasedbefore the deterioration of each device. The initial luminance of devices was improved by 50% to 70% and the time taken to increase to the maximum value decreased with the extension of processing time. The results indicate that the water vapor treatment is effective to optimize the performance of QLEDs. The lifetime of all devices wascalculated by the life formula, and the comparison of each deviceshows that the treated devices have a longer life than others. (The lifetime is about 1.7 times of the untreated device) As the processing time increases,the decrease of the maximum luminance and the intensifieddeteriorationare attributed to the negative effects on the organic materials of water and the new defect states generated during the oxidation of the quantum dots by the water molecules.In summary, the water vapor treatment optimizes the performance of QLEDs, which is beneficial for the research of the aging mechanism of the QLEDs and the simplification of the packaging process.