The invention discloses a preparation method of brinzolamide and its intermediate. The preparation method of the present invention comprises the following steps: in a solvent, carry out the following deprotection reaction on the compound of formula D and thiolate; wherein, in the compound of formula D, X is selected from O or NMe; X is When O, Y is Me, when X is NMe, Y is H; n is selected from 0, 1, 2, 3, 4 or 5; each R is independently NO 2 or CN; the thiol salt is the salt formed by thiol and metal, expressed as RS ‑ m + ; among them, M + Is an alkali metal ion, specifically can be selected from Li + 、Na + 、K + 、Ru + and Cs + One or more of; R is C 14‑24 alkyl. The preparation method of the invention has the advantages of simple and convenient operation, mild reaction conditions, high yield and good product quality, and is suitable for industrialized production.