Triterpenoid saponins are the main components of licorice,which have extensive biological and pharmacological activities,including hepatoprotective,antiviral and anti-inflammatory effects. In order to study the relationship between the structure and hepatoprotective activity of three saponins,the density functional theory (DFT) B3LYP method with 6-31+G* basis set was used to optimize the structure of glycyrrhizin (GL),glycyrrhetic acid monoglucuronide (GAMG) and glycyrrhetinic acid (GA). The properties of triterpenoid saponins have been discussed in detail based on their molecular structures,NPA charges,dipole moments,solvation energies and the energies of the frontier molecular orbitals. The results showed that the active sites of the three saponins were pentacyclic triterpenes,while the sugar ring was not the pharmacologically active site. However,the structure and the number of sugar ring would affect the physicochemical properties of drug molecules. The results showed that the frontier molecule orbitals were important for hepatoprotective activity,the lower energy gap between HOMO and LUMO ΔE(LUMO-HOMO),the stronger activity of the compounds would be. As a result,it was revealed that the hepatoprotective activity of the compounds goes along with the series GA>GAMG>GL. The calculated results were in good agreement with the experimental results.