The invention relates to a measurement 
system and a measurement method for a 
derating curve of an LED (light-emitting 
diode), belonging to the technical field of detection on thermal properties of 
semiconductor optoelectronic devices. According to the measurement 
system disclosed by the invention, the LED to be tested, a 
thermocouple and a clamp are arranged in a constant-temperature oven, and the LED to be tested and the 
thermocouple are arranged in the same position on the clamp. A digital source meter is connected with the LED to be tested, and a digital universal meter is connected with the 
thermocouple. The digital source meter, the digital universal meter, the clamp and the constant-temperature oven are respectively connected with a computer. The digital source meter is used for providing 
forward current for driving the LED to be tested; the constant-temperature oven is used for providing a stable 
environmental temperature; the thermocouple is used for detecting the actual 
environmental temperature in the vicinity of the LED to the tested; the digital universal meter is used for patrol inspection on the resistance of the thermocouple; and the computer is responsible for collecting and 
processing related data and outputting the graphical 
derating curve to a user. Compared with the prior art, the measurement 
system and method disclosed by the invention have the advantages of high efficiency, accuracy and a wide range of applications.