Abstract: In order to enhance the sensitivity of high power microwave detector and reduce the impact of ambient temperature, research of hot-carriers detector in liquid nitrogen was carried out. Kovar alloy was used in the BJ-100 waveguide HPM detector to enhance the ability of resisting temperature change. The binding force is bigger than 4.9 N in the test. Sensitivity experiments of the HPM detector at room temperature and in liquid nitrogen were conducted using the microwave source. Waveform of the HPM detector is consistent with that of the Schottky detector. The relative sensitivity of the HPM detector in liquid nitrogen is 20 times higher than that in the room temperature under the constant current, and the output voltage amplitude can be above 1 V.