The invention provides application of glycyrrhizic acid and a pharmaceutically acceptable salt thereof to preparation of antidepressant drugs, and specifically, application of the glycyrrhizic acid and the pharmaceutically acceptable salt thereof to preparation of the antidepressant drugs as a sole active component, application of the glycyrrhizic acid and the pharmaceutically acceptable salt thereof as an antidepressant drug synergist or application of the glycyrrhizic acid and the pharmaceutically acceptable salt thereof to treatment of treatment-refractory depression with combined application of the antidepressant drugs. According to the invention, clinical tests show that the glycyrrhizic acid and/or the pharmaceutically acceptable salt of the glycyrrhizic acid can achieve obvious synergistic effect on the antidepressant drugs and can rapidly, safely and effectively improve symptoms of depression in clinical application; therefore, the glycyrrhizic acid and/or the pharmaceuticallyacceptable salt of the glycyrrhizic acid can be used as the sole active component for preparing the antidepressant drugs, can be used for preparing the antidepressant drug synergist or can be appliedto treatment of treatment-refractory depression with combined application of the antidepressant drugs, can be applied to treatment of different depression, can improve the antidepressant effects of the drugs, is cheap, easily available, safe and non-toxic, and has good clinical application prospects.