In the paper a new OLED is provided. By adjusting the thickness of each layer in OLED the peak spectral wavelength moves to red. To explain the phenomenon a new simulation is presented to research the relation between thickness of the layer and their CIE coordinates. We use optical transmission matrix to deal with multiple layers. As a result, we obtain the relationships between the CIE coordinates of the device and the thickness of each layerIn this paper, we provide such a theoretic analysis.