Terahertz (THz) band is a frequency range starting from 0.1 THz to 10 THz. It is considered a new frequency band resources for future communication systems. However, the high absorption attenuation of THz waves in the atmosphere makes utilizing this frequency range very difficult. Current research on THz has rarely focused on satellites, aircraft, or other long-distance communications. Moreover, due to the channel model's limitations, some research cannot easily be applied to the entire THz band. So in this paper, we analyze the atmospheric attenuation on the propagation of THz waves in the long-distance scenario with a universal model. Then we propose a new non-orthogonal multiple access (NOMA) scheme (direct NOMA) according to the atmospheric attenuation. Through simulation, we analyzed the system capacity and the bit error rate of the three multiple access schemes (conventional NOMA, direct NOMA, and OMA) in this scenario. The simulation result verified the feasibility of THz in this scenario, and it points out that direct NOMA can increase the capacity and reliability of this system.