The origin of the efficiency drop of quantum dot light-emitting diode (QLED) under consecutive voltage sweeps is still a puzzle. In this work, we report the voltage sweep behavior of QLED. We observed the efficiency drop of red QLED with ZnMgO electron transport layer (ETL) under consecutive voltage sweeps. In contrast, the efficiency increases for ZnO ETL device. By analyzing the electrical characteristics of both devices and surface traps of ZnMgO and ZnO nanoparticles, we found the efficiency drop of ZnMgO device is related to the hole leakage mediated by trap state on ZnMgO nanoparticles. For ZnO device, the efficiency raise is due to suppressed electron leakage. The hole leakage also causes rapid lifetime degradation of ZnMgO device. However, the efficiency and lifetime degradation of ZnMgO device can be eliminated with shelf aging. Our work reveals the distinct voltage sweep behavior of QLED based on different ETLs and may help to understand the lifetime degradation mechanism in QLED.