The invention relates to a pharmaceutical use of ethoxy-substituted silibinin for inhibiting herpes simplex virus. More particularly, the invention relates to an ethoxy-substituted silibinin derivative on a ring B, namely, the use of compound (cis-trans)2-(2, 3-dihydro-3-(4-hydroxyl-3-methoxyphenyl)-2-hydroxymethyl-8-ethoxy-1, 4-benzo dioxane-6-)-2, 3-dihydro-3, 5, 7-trihydroxy-4H-1-chromene-4-ketone) or pharmaceutically acceptable salts thereof in the preparation of medicines for the treatment of virus infection and/or canker sore caused by the herpes simplex virus HSV-1. The compound is acquired by synthesis according to chemical methods, and pharmacological experiments show that the compound has strong inhibition effect on the herpes simplex virus HSV-1 with the IC50 value thereof being 41.07 microgram/milliliter.