Due to the various advantages on illumination, high-power light emitting diode (LED) system has been focused recently. Because the light source that consist of red, green and blue LEDs can provide full high definition color gamut with advantage of longer lifetime, LED light source starts to be applied in digital display system. However, much heat is dissipation from LED and operating temperature severely influences the characteristics of LEDs including dominant luminosity wavelength, luminosity and lifetime. Therefore careful thermal management is crucial to ensure accurate image quality of display device as well as guaranteed lifetime. The present study is conducted to investigate the performance of thermal management system for LED light source in rear projection TV. The result shows that the reducing thermal resistance between LEDs and substrate is the most effective way to dissipate heat and the applicable limit of thermal resistance is existed for various heat-dissipating condition of LEDs. And it is also suggested that the efficacy of heat transport system from LED to ambient applied in red, green and blue LED light system to ensure the product quality.