The phosphorescent electroluminescent devices were developed by doping different proportions of fac-tris-2-phenylpyridine iridium (III) (Ir(ppy)3) into PVK as a light-emitting layer. Through the research of the luminescence mechanism, it is found that in the process of photoluminescence (PL), Fo¨ster energy transfer mechanism plays a dominant role, and in the process of electroluminescence (EL), the two types of energy transfers as Dexter energy transfer and charge trapping affect the luminescence performance. The I-V-L characteristic of the device shows that the lightpower efficiency is highest and the energy transfer is the most efficient when the doping proportion of Ir(ppy)3 is 5%.