It is necessary to use thin film encapsulation for protecting the organic emitting device of the flexible display from the oxygen and moisture permeation. The optical properties of the OLED device protected by thin film encapsulation have been investigated. It was found that the chroma of the emitting light of the OLED device was changed by the thin film encapsulation. The thin film encapsulation influenced the emission spectrum of the OLED device. The optical length of the micro-cavity of the emitting device was adjusted to compensate the variation of the chroma.