The invention relates to application of m-chlorobenzoyl substituted dehydrosilybin for preparing antiviral drugs, in particular to medicinal application of a 2-3-position m-chlorobenzoyl substituted 2,3-dehydrosilybin ester derivative, namely a compound of m-chlorobenzoic acid [3-(4-hydroxy-3-methoxyphenyl)-6-(3,5,7-trihydroxy-4-oxo-chromene-2)-2,3-dihydro-1,4-benzodioxane-2]-methyl ester or a pharmaceutical salt thereof in the preparation of medicaments for controlling viral infections and/or oral ulcers caused by herpes simplex virus HSV-1. The compound is prepared by semi-synthesis of a chemical method, and pharmacological experiments show that the compound has definite inhibition on the herpes simplex virus HSV-1, and the half inhibition concentration IC50 value is 44.78 micrograms per milliliter.