The output level of 12.5 μm HgCdTe detector is very sensitive to the working temperature, so it is necessary to study the temperature sensitivity. When doing experiments, adjust the working temperature of the detector, collect its output level and analyze the data. It can be seen from the analysis results that the variation of working wavelength and dark current with temperature is the main factor leading to the change of output level. The best working temperature of the 12.5 μm HgCdTe detector is around 60 K. The experimental method is simple to operate and does not require complicated operating equipment. Most infrared laboratories can meet the experimental requirements.