The invention relates to pharmaceutical application of Cordyceps sinensis and provides application of Cordyceps sinensis in the preparation of drugs for preventing and / or treating yellow fever virus infections; the drugs include Cordyceps sinensis as an active ingredient and one or more pharmaceutically acceptable excipients, the Cordyceps sinensis is selected from natural Cordyceps sinensis, fermented Cordyceps sinensis mycelia and extract of the natural Cordyceps sinensis and fermented Cordyceps sinensis mycelia, and the extract is one, or a combination of any, of aqueous extract, alcohol extract, ester extract, ether extract and chloroform extract. Inhibition experiments on yellow fever virus prove that Cordyceps sinensis has good inhibition effect, and therefore it is proved that Cordyceps sinensis may be used to prevent and / or treat yellow fever virus infections and has the advantages such as significant effect, low side effect and high acting speed. Therefore, Cordyceps sinensis can be used to develop drugs for treating diseases due to yellow fever virus and has great social benefit and research value.