A THz wave atmospheric transmission and attenuation model is developed based on the radiation transmission theory, continuum absorption and modified Van Vleck-Weisskopf(VVW) line-shape combining with the HITRAN database. The absorbing attenuation characteristics are compared to Millimeter-wave Propagation Model(MPM). The new method of zenith stratification is added, which forms the numerical simulation ability of atmospheric vertical transmission attenuation and dispersion for broadband THz wave. The attenuation characteristics and window structures are studied at different distances. As a result, the attenuations of 340 GHz and 410 GHz atmospheric windows are less than 25 dB and 45 dB respectively. In addition, the group velocity dispersion is low, which enables the feasibility of signal transmission.