The organic light emitting diode with inserted LiF layer has been fabricated. Tris-(8-hydroxyquinoline) aluminum (Alq3) was used as electron-transport layer and N, N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (NPB) was used as hole-transport layer. By changing the thickness of LiF deposited between Alq3 and NPB, the optoelectrical properties and the magnetic field effect on electroluminescence were studied at different temperatures. The measurement results show that using LiF layer enables the transport of carrier and the formation of excited states inside the device. A thick LiF layer blocks the transport of holes, lowering the efficiency of the device. However, use of LiF layer can effectively tune the magnetic field effect of electroluminescence. Compared with conventional devices, the magnetic field effect of device with inserted LiF layer was strengthened within low-field range (the magnetic induction BB≥40 mT) decrease of electroluminescence, and the thicker the LiF layer, the smaller the magnitude of decrease. These observations indicate that the concentration of the triplet excitons offects the high magnetic field decrease of electroluminescence at low temperatures.