Abstract: The terahertz wave provided greater communication bandwidth and capacity than millimeter. Compared with the visible light and the infrared light, THz pulses had longer wavelength propagating in the random medium, not only caused the temporal and spatial deformation, but also affected on the incident particle scattering, then the pulse signal attenuation occurred. Based on the Mie theory, using the discrete distribution of particles with the random wave transmission and scattering theory, the extinction coefficient of fog droplet in the terahertz wave was calculated. And the extinction coefficients of different wavelengths of terahertz wave change with the particle size were analyzed. Considered the droplet particle size distribution, the average albedo and phase function were obtained under different wavelengths. Finally, propagation characteristics of terahertz signals in fog particles by different visibilities were analyzed. The result shows that in the atmospheric environment, the absorption and attenuation of fog in terahertz wavelength can not be ignored, the imaginary part of the refractive index changes greatly with different wavelengths, and the transmission of the THz wavelength in fog is seriously impacted.