A new class of multiple quantum well (MQW) perovskites light-emitting diodes (PeLEDs) has been demonstrated, which have high external quantum efficiency (EQE) and good stability, indicating MQW perovskite is promising for realizing high performance PeLEDs. However, as other LEDs, both the EQE and energy conversion efficiency of MQW PeLEDs decrease monotonically with increasing current density after peak efficiency, which is detrimental for displays requiring efficient operation at high brightness. In particular, in MQW structures, the charge carriers are concentrated in the quantum wells with lower bandgaps, which only occupy a small portion of the MQW film, thereby the local carrier density is much higher than the total carrier density. We introduce mixed-cations to control the constitution of MQW perovskites, which increases the width of quantum wells and leads to reduced efficiency roll-off. Moreover, due to the stable structure of mixed-cations, the device lifetime (half of the initial brightness, T50) reaches ~30 hr under a constant current density of 10 mA cm-2.