The results simulated the I-V curves fo OLED which are whichever suitable to revised F-N model with built-in electrical field E i or trap-charge-limited current (TCL) model,indicate that the defect states exist in OLED.They have influenced the I-V characteristics of the OLEDs.For simulating of some OLED obeyed revised F-N model,we have to use an inner building electric field E i varied with bias for simulation of the I-V curves.For simulating of some OLED obeyed TCL model,then we can see a "hesitated I-V curve" which is similar as in semiconductors devices with defect states.The hesitated I-V characteristics will drift with applied voltage and have some ability to be recovered.These effects would cause form and can be explained by the charges trapped in or draw-out from the defect-states with applied voltage.