Based on the High-resolution Transmission (HITRAN) molecular spectroscopic database, the absorptions of the THz wave by the main atmospheric molecules were contrasted. According to the Mie theory and with the fog particle size distribution considered, the average scattering characteristics of fog droplet particles were analyzed with different incident wavelengths. The transmissivity and the reflectivity and the forward and backward scattering intensities of the THz signal in fog,as well as the infrared light, were investigated with Monte Carlo method. The result shows that in THz region, the lower the frequency, the higher the transmissivity, the lower the reflectivity, the weaker the backward scattering intensity; additionally, with a same distance the THz wave has a better transmission capacity than the infrared light; meanwhile, the forward scattering intensity of the infrared light is stronger than the THz wave with a same scattering angle. The research in the paper is of great significance to the application of the terahertz technology on the atmospheric space.