The invention relates to 4,5-dihydro-thiazinogeldanamycin which is a new geldanamycin derivative obtained by genetic engineering technology, and a preparation method thereof. The new derivative is obtained by constructing a geldanamycin producing strain streptomyces hygrocopicus 17997 P450 monooxygenase gene (gdmP) blocked mutant and performing fermentation and extraction; and a research result shows that the 4,5-dihydro-thiazinogeldanamycin has antiviral activity and extremely high water solubility and is expected to be developed into a clinically useful antiviral medicament.