High power LED devices based on eutectic welding process and COB packaging technology were simulated by using ANSYS finite element analysis software. The thermal performance of COB packaging device and traditional discrete device, as well as eutectic welding process and adhesive bonding process, were contrastively analyzed. Simulations indicate that, the thermal resistance can be lowered by using COB package and eutectic welding process. The chip temperature rises with the decrease of the chip interval. When the thickness of the bonding layer increases, the chip temperature also rises, while the maximum thermal stress decreases. Combining the COB packaging technology with the eutectic welding process can effectively improve the thermal characteristics of high power LEDs. Determining the proper chip interval and thickness of the bonding layer can further improve the thermal characteristics.