The THz spectrum of orotic acid is measured in the range of 10-120 cm-1 by using Terahertz Time-Domain Spectroscopy(THz-TDS). The result shows three distinct THz absorption features which are interpreted by density functional theory. It is found that the feature at 95.5 cm-1 originates from the combination of intermolecular and intramolecular vibrational modes while the rest two features come from the rotational modes. Besides, the intermolecular interactions of orotic acid may minimize the intramolecular interactions to a certain extent. These results may be helpful to the monitoring of orotic acid in the industrial production and its study on pharmacological characteristics.