Vacuum packaging technology is one of the main packaging methods for extended wavelength InGaAs detectors,thermoelectric coolers used to provide a low temperature environment for the focal plane of extended wavelength InGaAs detectors.The performance of the two stage thermoelectric cooler under the condition of vacuum packaging technology without thermal load was tested.The relationship between the cold and hot end temperature difference and the thermal load of the two stage thermoelectric cooler at different input currents (power) was studied.The refrigeration performance of the two stage thermoelectric cooler under low temperature conditions and the apparent thermal conductivity of the two stage thermoelectric cooler when it is not working were tested.The results show that when the heat sink temperature is 274 K,the cold end can reach 221.4 K and the cold and hot end temperature difference is about 77.5 K.When the input current is constant,as the thermal load increases,the temperature difference between the cold and hot end decreases linearly,and the slope increases with the increase of the input current.The temperature difference between the cold and hot end of the two stage thermoelectric cooler is larger at higher temperatures,that is,the refrigeration performance is better;when the temperature is 233.1 K and 249.8 K,the apparent thermal conductivity is 11.30 W/(m·K) and 8.29 W/(m·K)respectively.