A series of single-unit and tandem blue phosphorescent organic light-emitting diodes (OLEDs) were prepared by ad-justing the concentration of dopant based on the structure of ITO/NPB/EL unit/Alq3/Cs2CO3/Al. The results show that tandem device with doping concentration of 10 wt% has appropriate energy transfer, which achieves the best perfor-mance with a maximum current efficiency of 3.4 cd·A-1. Further study found that current efficiency and power effi-ciency of the tandem OLED adding BCP as hole blocking layer (HBL) can achieve 7.85 cd·A-1 and 0.72 lm·W-1, re-spectively. It is 2.88 times and 1.57 times larger than those of sing-unit devices, and green peak is restrained effective-ly.