Abstract: In order to study the dependence of optical and electronic performance of Organic Light Emitting Diode （OLED） on working parameters, the experimental data of ITO/TPD（50nm）/Alq₃ （50nm）/Mg/Al were analyzed. It is found that the conduction type of the device is injecting current limited in low voltage area and trap charge limited （TCLC） in high voltage area. According to combination theory, F₂/J （electronic field intensity F and current density J） is used to relate quantum efficiency with current density directly.