Impurities are one of the important factors affecting the performance of HgCdTe devices. For CdZnTe substrate crystals and narrow bandgap HgCdTe materials, the impact of impurities is more significant. The common impurity types in HgCdTe materials and the role of impurities in the materials are mainly discussed. The main impurities that affect the performance of the device are analyzed. Glow discharge mass spectrometry (GDMS) is used to test the impurity content in the material. At the same time, the impurity content in the CdZnTe substrate and the HgCdTe thin film material grown by liquid phase epitaxy is reduced through the improved zone melting process. The electrical performance of HgCdTe thin film is improved to meet the preparation requirements of high-performance HgCdTe infrared detectors.