Terahertz waves have unique properties and applications, but there are physical limitations such as atmospheric attenuation and so on. Since the main attenuation of terahertz transmission in the atmosphere comes from water vapor, terahertz time-domain spectroscopy was used to conduct terahertz time-domain spectroscopy measurements in different air humidity at the frequency range of 0.1-2.0 THz by building terahertz time-domain spectroscopy system with different stroke (0.5 m, 1 m, 2 m, 3 m), respectively. 25 absorption of water and 10 windows of THz waves were obtained. The results show that: with the increase of transmission itinerary or humidity, absorption band is broadened and terahertz window is compressed. The study provides the basis for the potential applications of ultra-broadband terahertz waves.