Three red microcavity organic electroluminescent devices (MOLED) with different thicknesses were designed and fabricated,the device structure was as follows:Glass/DBR/ITO (thickness of 150,182,and 196 nm respectively) / NPB (82 nm) / DCM-Alq3 (71 nm) / Mg-Ag (70 nm). With the increase of ITO layer,the cavity length of microcavity devices increased accordingly,and the devices' resonant mode (light-emitting peak) changed from 604 nm to 640 nm and then to 656 nm,CIE color coordinate changed from (0.52,0.48) to (0.61,0.37) and then to (0.61,0.38),indicating that the color purity increased gradually. The optimal electroluminescent performance was observed in the sample with the ITO thickness of 150 nm,the emitting center wavelength was 604 nm,the maximum brightness reached 32008 cd/m2,and the maximum current efficiency was 3.15 cd / A. It shows that the ITO thickness of the microcavity light-emitting devices affects the microcavity OLED’s light-emitting properties a lot due to the micro-cavity effect.