In this paper, based on the terahertz time-domain spectroscopy (THz-TDS), the tert-butyl alcohol solutions with different concentrations were measured, and the curves of the absorption coefficient from 0.3 to 1.0 THz were obtained. The difference between the experimental results and theoretical calculation were analyzed by model of packing density. It is concluded that under the proper conditions, using THz-TDS technology for testing and data analysis, the hydration number of tertiary butyl alcohol solution can be calculated effectively. These results are valuable for the later analysis of the solution system of alcohol molecules.