Herein, a series of blue organic electroluminescence devices are fabricated with 4,4',4″-tris(N-carbazolyl)triphenyl-amine (TCTA), N,N'-dicarbazolyl-3,5-benzene (mCP), and 1,3,5-tri(m-pyridin-3-ylphenyl)benzene (TmPyPB) as the host materials. Owing to the different lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) energy levels of the host materials, a structure in the light-emitting layer (EML) with different energy level gradients is formed by changing the host materials and the number of EMLs. The effects of different EML structures on the performances of blue phosphorescent organic light-emitting diode are investigated. Among them, the double light-emitting layer device A3 with the host materials of TCTA and mCP obtains the best performance, and the maximum current density, the maximum current efficiency, and maximum luminance are 134.94 mA/cm ², 40.28 cd/A, and 12070 cd/m ², respectively. Among all devices, device A3 also exhibits the characteristics of low turn-on voltage (3.25 V) and low efficiency roll-off.