In this paper, we study the phase shift of the reflection from a semitransparent electrode of a top-emitting organic light-emitting device (TOLED) which is able to adjust spectrum of TOLED. Based on the micro-cavity theory and the transfer matrix theory, a model is set up to simulate the red TOLED. The simulation results show that the modulation of the device is not only limited to organic layer thickness, but also related to the reflection phase shift. The phase shift of the reflection of top electrode is adjusted through changing the thickness of organic layer capped on the top electrode, thus the TOLED optical performance can be changed. This result provides a useful method of improving the performance of the device.