Abstract: A pharmaceutical composition for producing a safe amount of nitric oxide (NO) in vivo and use thereof. The pharmaceutical composition comprises the following components: an NO toxicity decreasing agent, an NO extender, and a nitric oxide synthase inducer. Provided is the pharmaceutical composition which has high versatility and extremely effectively treats pathogenic microorganism infections. The NO toxicity decreasing agent is selected from 5-methyltetrahydrofolic acid, NMN, and dehydroascorbic acid; the NO extender is selected from arginine; and the nitric oxide synthase inducer is selected from phytohemagglutinin. Provided is a new medicinal activity of the 5-methyltetrahydrofolic acid, having a variety of active effects on an immune system caused by pathogen infection, and capable of being used for treating or preventing disease caused by virus infections and other pathogen infections. In particular, the composition is used for preventing or treating African swine fever.