The Joule heating inside organic light-emitting devices(OLEDs) is part of the device degradation factors. Therefore, it is very important to study the thermal characteristics of OLEDs for effective heat dissipation. So the thermal characteristics of OLED were simulated via the solid heat transfer module of COMSOL finite element analysis software. It is found that the device temperature increases linearly with the input power. At driving current of 150 mA·cm-2, the highest temperature of the Alq3 emitting layer and bottom surface of the glass-substrate are 82.994 3 ℃ and 77.392 6 ℃, respectively, the highest temperature at the central region of the cathode surface is 82.994 2 ℃, and its average temperature is 78.445 ℃. Thermal analysis simulated results show the temperature distribution and thermal characteristics of an OLED can be affected by changing the thermal conductivity and thickness of functional layer, convection heat transfer coefficient, and surface emissivity. When increasing the substrate thermal conductivity, the temperature of the OLED is significantly reduced, and the surface and internal temperature gradients are greatly reduced; When improving the air convection heat transfer coefficient and the surface emissivity of the substrate, the temperature of the OLED can be greatly reduced. However, other parameters have no significant effect on improving thermal characteristics for the OLED.