The detection of food and medicine has important application value in the field of education and civic. Therefore, a detection method based on terahertz time-domain spectrum analysis is proposed. The terahertz time-domain spectroscopy detection technology is used to study the terahertz spectrum characteristics of materials covered by different packages, and the detection technology of terahertz samples under high relative humidity conditions is studied. A simple and effective spectral subtraction method is used to deal with the water vapor absorption interference in the sample spectrum, and to calculate the refractive index and absorption coefficient of the sample in the terahertz band. By calculating the refractive index and absorption coefficient of the samples shielded by different wrappers, the proposed method can accurately distinguish the types of samples.