According to the changes of the fluorescence spectra in PVK thin films after doping, it is indicated that the energy transfer between PVK and perylene was occurred in electroluminescence of doped PVK thin films. A model Hamitonian was presented to describe the luminescence of PVK after doping. It was found that the effective energy transfer between PVK and perylene is derived from the charge transfer between them. The maximum amount of transferred charges occur at a certain dopant concentration for a given doping PVK, and the occurrence of plateau region is due to the saturation at dopant concentration. The results are in good agreement with experiments.