Millimeter wave is widely used in communication, radar, remote sensing and astronomy. In order to successfully design and develop a millimeter wave system with excellent performance, it is necessary to understand the atmospheric propagation characteristics of millimeter wave under different meteorological conditions. There is no precise definition of millimeter wave frequency band. The electromagnetic wave in frequency domain (wavelength 1-10 mm) of 30-300ghz is usually called millimeter wave. It is located in the wavelength range where microwave and far-infrared wave overlap, so it has the characteristics of two kinds of spectrum. The theory and technology of millimeter wave are the extension of microwave to high frequency and the development of light wave to low frequency.