An experimental study on the performance organic elecroluminescent device was presented.Four organic electroluminescent devices(OLEDs) with different thickness of LiF layer A:ITO/Alq_3/Al,B:ITO/Alq_3/LiF:Al (1 nm),C:ITO/Alq_3/LiF:Al (1.5 nm),and D:ITO/Alq_3/LiF:Al (2 nm) were fabricated by vaporing method.And the effects of LiF layer on the properties of cathode/Alq_3 interface and the performance of OLEDs had been intensively investigated.It was shown that OLEDs with 1.5 nm LiF layer not only could improve the properties of cathode/Alq_3 interface but also could enhance the brightness of OLEDs such as at the applied voltage 10 V,the barrier height of cathode with 1.5 nm LiF/Alq_3 interface was only 3.12 eV,and its brightness was acheved the maximum value 800 cd/m~2,etc.