In the paper a new method is presented to simulate the course of light output from organic light emitting device. The method uses optical transmission matrix to deal with multiple layers. To confirm the validity of our theories, a comparison of the theoretic analysis with testing results is given. The calculated curve consistented with the experimental value. By this methoed the Commission Internationale de L'Eclairage （CIE） coordinates of device were simulated. By adjusting the thickness of each layer in organic light emission diode (OLED) we obtained different CIE coordinates. When thickness becomes thicker the CIEX becomes bigger on the other hand CIEY become smaller.