Rare earth complex Tb(aca)3phen is synthesized and characterized by ultraviolet-visible absorption spectrum, and the absorption range is mainly from 250 nm to 355 nm, which has two absorption peaks located at 296 nm and 345 nm. The photoluminescence spectra of the material show bright green emission under the excitation of 345 nm light and four emission peaks are located at 487, 545, 585, 621 nm, which correspond to the 5D4→7F6, 5D4→7F5 , 5D4→7F4, 5D4→7F3 electron transitions. A series of organic light emitting diodes (OLEDs) based on Tb(aca)3phen as emission layer are fabricated, the devices′ structure is ITO/PEDOTPSS/Tb(aca)3phenPVK/Bphen(x nm)/Al. The effect of Bphen layer thickness on the performance of OLEDs is investigated. The recombination of hole and electrons can be increased when the thickness of Bphen is about 5 nm. The luminescent power of OLEDs is 2.4 times as large as that of OLEDs without Bphen buffer layer under 20 V driving voltage.