To measure the thermal characteristics of LED, one method based on the structural function theory was studied. Thermal test equipment was used to measure the transient temperature curve of LED samples by changing the power input of LED. Then, the parameters such as thermal resistance and thermal capacitance can be analyzed through structure function extracted from the temperature curve. Compared with conventional methods, the method has the nondestructive advantages. Furthermore; it can measure more accurately the distribution of each part of the LED with good visual effect. So it is one of the effective means to evaluate the thermal characteristics of high power LED.