LED has promised to replace conventional light sources with impressive economic and environmental saving because of the realization of high efficiency and long life time light sources. Reliability issue is a key factor affecting the lighting quality and life time of LED lighting system. Each LED system includes two major aspects; optical and electrical driver. The LED driver is one of the weakest components in the LED luminaries and they tend to degrade rapidly with increasing temperature. The effect of temperature on performance and reliability of LED driver is analyzed in this paper. A thermal simulation model based on tapped-inductor quasi-resonant Buck LED driver was set up. The thermal field and thermal stress analysis of the driver was done by using the software EFD Pro 8.2. The losses from various components of the driver were calculated in detail. The histogram of losses in various components in the driver was given. Computer simulation and a prototype rated at 5 W, with an input ac voltage of 176–265 Vrms and an output current of 700 mA has been implemented to verify the prediction.