Terahertz wave at frequency range from 0.1 THz to 10 THz has advantages such as large transmission capacity, good direction, high transmission efficiency and so on. Studying the application to the communication field plays a very important role in satisfying the demand of higher transmission rate for users. The terahertz time-domain spectroscopy (THz-TDS) system is used to measure the terahertz wave transmission data from 0.1 THz to 2.4 THz in atmosphere with different humidities for a 0.6 meters transmission distance. And based on the classical model of extracting optical constants proposed by Dorney et. al., the data such as delay time, power spectrum, amplitude spectrum and absorption coefficient are obtained. The results show that the water vapor in the atmosphere has obvious absorption and attenuation effects on terahertz, and the attenuation rises with the increase of humidity, especially in absorption peak. At the same time, there is transparent window of weak attenuation which can be applied to terahertz communication.