In the late 1950s, the invention of mercury cadmium telluride (HgCdTe) alloy semiconductor material built the foundation of thermal imaging technology and its engineering applications. In 1975, the United States put forward the concept of common thermal imaging modulars——Modular Common Thermal Night Sights based on the first-generation infrared detector. Since then, HgCdTe materials and detectors have been widely applied in the military field. In this paper, the advantages of HgCdTe detector were analyzed from the perspectives of the basic physical properties of HgCdTe material. It was convinced that HgCdTe detector was still the best infrared detector. Furthermore, diversified HgCdTe detector technologies had been developed, which including but was not limited to large area array, planar junction and heterojunction, dual band, very long wavelength, 150 K operating temperature, avalanche detector, etc. With the emerging of the new structure, new mode, new mechanism, new method and new technology, HgCdTe materials and detectors would be promoted to a new height and was the mainstream candidate of the fourth-generation infrared focal plane detector.