Blue-emitting materials and their light-emitting diodes (LEDs) are always challenging in lighting and display applications. Recently, perovskite LEDs (PeLEDs) with efficient and stable green/red emission have made great progress, where external quantum efficiency (EQE) over 20% has been reached. However, it is still a big challenge to realize stable blue PeLEDs with high efficiency mainly because of the poor film quality and unreasonable device structure. Herein, a cocktail strategy, that is, multication (Cs/Rb/FA/PEA/K)Pb(Cl/Br)3, is demonstrated to improve both the efficiency and stability of blue PeLEDs. Combined with the "insulator-perovskite-insulator" structure, PeLEDs based on a multication (Cs/Rb/FA/PEA/K)Pb(Cl/Br)3 perovskite film show maximum EQE of 2.01% and maximum luminance of 4015 cd/m2 at 484 nm. More importantly, the device exhibits robust durability, and its half-lifetime is over 300 min under continuous operation. The multication strategy could open up a new avenue for the design of new blue-emitting materials for high-performing PeLEDs.