THz atmospheric transmission is an important part of science and technology,which has permeated into almost all applications of terahertz technology. Research on terahertz atmospheric transmission is nearly on horizontal level in the existing literature. A dispersion attenuation model of terahertz atmospheric transmission is presented based on the radiation transfer, dispersion theory and Van-Vleck Weisskopf line-shape combined with Jet Propulsion Laboratory(JPL) database. The absorbing attenuation characteristics of terahertz atmospheric transmission along the slant path between 0.1 THz and 1 THz are studied using this model and compared with the existing literature. The influences of water vapor with different densities on the amplitude, phase and spectrum of the transient terahertz pulse are analyzed. Three relatively stable atmospheric transmission windows in 0.14 THz-0.17 THz,0.19 THz-0.32 THz and 0.32 THz-0.37 THz are obtained. This work has provided a theoretical reference for terahertz time-domain communications and space transmission.