In order to judge the authenticity of the drug and to check the purity of the drug, and to overcome the shortcomings of the long time consuming, sample loss and complicated operation in the current qualitative and quantitative detection of chemical drugs, a fast, quasi determinacy and quantitative method for drug detection based on terahertz spectroscopy is proposed. Based on the terahertz absorption spectrum, the characteristic peak frequency points and the area difference of loratadine and racecadotril were extracted. The qualitative and quantitative detection of the drugs was carried out by using these information. In quantitative detection, stability and accuracy of terahertz spectrum are high. In the establishment of concentration gradient, the linear fitting correlation coefficient reaches 99.8%. Meanwhile, principal component analysis (PCA) was used to detect other drugs. The results showed that the accuracy of qualitative detection was 100%, and the error of quantitative detection was less than 0.01. These results can provide reference for the rapid, accurate and nondestructive testing of the following drugs.