Blue organic light emitting diode (OLED) with a graded junction at hole transporting layer (HTL) and emitted layer (EML) interface was constructed (Cell-GJ). Compared with conventional heterojunction OLED (Cell-HJ), it exhibited significantly improved lifetime, and the half lifetime achieved 8460 h at initial luminance 100 cd/m2, more than 6 times longer than that of Cell-HJ. This improvement is attributed to the elimination of local electric field across the non-abrupt heterojunction, which thereby decreases the production of Joule heat and enhances the lifetime of device. However, the efficiency of Cell-GJ is lower than that of Cell-HJ. In order to redeem the decrease in efficiency of Cell-GJ, another device with a GaQ thin layer inserted in the TBADN/AlQ interface was made (Cell-GJGaQ). For the LUMO energy level of GaQ is between the energy level of AlQ and TBADN, the multi-step energy barrier between AlQ-GaQ-TBADN improves the electron (minority) injection greatly, so the luminescence efficiency is greatly improved. This Cell-GaQ shows efficiency 20% higher than that of Cell-GJ and also 5 times longer half lifetime than that of Cell-HJ. The whole performance is greatly improved.