Organic light emitting devices (OLEDs) are easy to be influenced by water vapor,oxygen of air and other pollutants,whi ch leads to the reducing of their working life.In the paper,the MgF_2thin fil m with a good optical transmission and thermal stability and the Se thin film wi th a good stability in water vapor and oxygen were made in to composite thin fil m by vacuum evaporation as OLED encapsulation layer,and the lifetime of the devi ce would be improved in expectation.The MgF₂/Se thin film was vaporized on t he cathode surface in the same conditon of vacuum (3×10－4 Pa) after the deposition of functional layers in OLEDs was completed.The luminance-voltage- current densities and electroluminesce spectra of green OLEDs (the device struct ure is ITO/CuPc/NPB/Alq₃:C-545T/Alq₃/LiF/Al. )before and after encapsulation are compared.The research shows that the current density-voltage and electroluminesce spectrum of OLEDs are scarcely influenced by MgF₂/Se encapsulation layer and both of their spectra are at 528nm,the color coordinates are (0.3555,0.6131) and (0.3560,0.6104),respectively,and the t urn-on voltage is only changed from 3V to 4V.However,the lifetime of the devi ce with MgF₂/Se thin film is increased from 175h to 300h,about 1.7times o f the original.So the MgF₂/Se thin film is an effective inorganic thin film encapsulation layer for OLEDs.