The invention discloses an application of saikosaponin a in preparing medicaments for preventing and treating influenza in human and animals. Pharmacological experiments show that the saikosaponin a extracted from Chinese medicinal material Radix Bupleuri can remarkably inhibit in vivo and in vitro proliferation of influenza and avian influenza virus, protect mice infected with influenza and avian influenza virus, and can be used for preparing medicaments for preventing and treatment influenza in human and animals, with definite effective components and action mechanism, controllable quality, good safety, no toxicity and stable therapeutic effect. Also, the active ingredient saikosaponin a mainly plays roles by regulating inflammation signal pathway in host cells, so that an influenza virus strain is not easy to generate drug resistance.