In order to improve brightness and efficiency of red organic light emitting devices (OLEDs), highly efficient red tandem OLEDs have been fabricated by using AlQ3∶Mg/WO3 as interconnecting layer. The optimal device whose efficiency and luminance reach three times efficiency and four time of that of a conventional single-unit device respectively, is obtained by controling WO3 thickness. The device is fabricated by Eu(DBM)3bath and DCJTI units, with a structure of ITO/TPD/DCJTI∶CBP/BCP/Alq3/Alq3∶Mg/WO3/TPD/Eu(DBM)3bath∶TPD/Eu(DBM)3bath/LiF/Al and the maximum luminance of 8609 cd/m2 and the maximum efficiency of 10.2 cd/A are achieved.