The invention relates to a preparation method of a biological agent for preventing electromagnetic radiation. The biological agent is prepared from the following raw materials: stem of laevigate parameria, heartleaf houttuynia herb, fragrant solomonseal rhizome, barbary wolfberry fruit, bark of Chinese corktree, ginkgo leaf, perilla leaf, common ducksmeat herb, loquat leaf, glossy privet fruit, turmeric root-tuber and the like. The medicament prepared by the method provided by the invention is convenient to use, and has an effect of preventing radiation and an effect of assisting radiation damage treatment, and the used raw materials are common traditional Chinese medicinal materials in China and are widely distributed and low in price, which is one of advantages of applying the medicament to development application; and the biological agent has a wide application prospect.