Since the outbreak of novel coronavirus pneumonia (COVID-19), many research institutes and enterprises at home and abroad have been accelerating the research of COVID-19 (SARS-CoV-2) antibody drugs. However, the research on effective drugs was limited by the drug polymorphisms. The environment of drug production, storage and use also affected the stability of the drug. As a fast, non-destructive testing method, infrared spectroscopy can reflect the differences in drug structure, crystal form and even manufacturing technique to the vibration spectrum, which greatly improves the efficiency of R&D (research and development). In this paper, three clinical trials were considered effective drugs for the treatment of COVID-19: Chloroquine diphosphate, Ribavirin and Abidol hydrochloride. Their far-infrared spectrum (1~10 THz) and mid-infrared spectrum (400~4 000 cm^-1) were measured by Fourier transform infrared spectrometer (FTIR). In the far-infrared spectrum, the characteristic peaks of Ribavirin were around 2.01, 2.68, 3.37, 4.05, 4.83, 5.45, 5.92, 6.42 and 7.14 THz; the characteristic peaks of Chloroquine phosphate were near 1.26, 1.87, 2.37, 3.06, 3.78, 5.09 and 6.06 THz; the characteristic peaks of Abidol hydrochloride were located near 2.24, 3.14, 3.72, 4.25 and 5.38 THz. Based on density functional theory, the B3LYP hybrid functional and 6-311++G (d, p) basis sets were selected to analyze the vibrational modes corresponding to all characteristic peaks in the spectrum using Crystal14 and Gaussian 16 software, and the accurate identification of the vibration spectrum was realized. The vibrational modes originated from the molecules’ collective vibration in the far infrared region. In the mid-infrared band, below 2 800 cm^-1, the vibrational modes mainly came from the in-plane and out-of-plane bending and rocking of the group; Above 2 800 cm^-1, the vibrational modes transited to the in-plane stretching of C-H, O-H and N-H bonds. Taking the crystal structure with periodic boundary conditions as the initial configuration of the theoretical calculation would make the calculated spectrum more consistent with the experimental one, especially in the far-infrared band and the low-frequency band of mid-infrared (400~1 000 cm^-1). This study was of great significance to deeply understand the pharmaceutical characteristics, drug interactions, control of drug production process, and guide the storage and use of antiviral drugs such as Chloroquine phosphate, Ribavirin and Abidol hydrochloride.