Organic light emitting devices (OLEDs) have some performances, such as low power consumption, ultra-light, fast re-sponse speed, high-definition, self-luminous and viewing angle, etc, which are expected to become a mainstream of the next generation of display devices. It is found that the microcavity structure can narrow the luminescence spectrum of the thin film and improve the luminescence color purity of the device effectively. We prepared a light-emitting device by using high vacuum deposition process and high-precision film thickness detector. This paper designed and prepared the green OLED devices based on double metallic mirrors in microcavity structures, of which the process was by vac-uum evaporation and double metallic mirrors of devices: Al/MO3 as device of anode and hole injection layer, and LiF/Al as device cathode and electron injection layers.