The light extraction of OLED has been successfully enhanced by the combination of multi-cathode structure and high refractive index intermediate layer, which are introduced to control the surface plasmon coupling in the metal cathode and the distribution of optical energy in OLED, respectively. From the multi scale optical analysis, it was found that an approximately 70% of electromagnetic energy in the dipole emission was effectively converted to the glass and air modes. The phosphorescent green light emitting device exhibits higher light extraction by a factor of 1.6–1.7.