The basic principles of various test techniques for measuring the junction temperature of GaN-based light-emitting diodes (LED) were studied, including the pulse current method, the small current method and the optical imaging method. The reliabilities of different methods were compared. The results show that, at a large pulse current, the series resistance effect cannot be ignored, which leads to a rather lower average junction temperature. The small current method is able to reduce both the switching time between the heating current and the test current and the series resistance effect, which improves the measurement accuracy. The optical imaging method is based on the relationship between the light intensity and the junction temperature, which allows to obtain the spatial distribution of the temperature of devices, and could be helpful for fabricating high-quality LED.