Due to the electron carriers′ lower m obility and injection than hole carriers in regular organic light-emitting devi ces (LEDs),in o rder to improve the performance by enhancing electron injection and simplify the preparation process,we take Ca:Mg:Al ternary all oys as cathode in organic light-emitting devices and prepare a series of green phosphorescent organic lig ht-emitting devices with structure of ITO/MoO₃/NPB/TCTA/CBP:GIr1/TPBi/Alq₃/Mg(x%):Ca:Al.We compare devices with/without Mg in its alloy cathode and analyze the function of Mg in electron inject ion and balance of hole and electron carriers.We also optimize the cathode by adjusting the content of M g in ternary alloy cathode,thus maintain devices with maximum luminance of 41830cd/m^2and excellent current efficiency around 26cd/m 2.