The invention discloses a monohydroxy sugammadex sodium preparation method, which specially comprises: 1, carrying out monoacylation on gamma-cyclodextrin by using substituted benzoyl chloride to obtain gamma-cyclodextrin monoester; 2, carrying out a halogenation reaction and a hydrolysis reaction on the gamma-cyclodextrin monoester to obtain hepta-halogenated gamma-cyclodextrin; and 3, carrying out a reaction on the hepta-halogenated gamma-cyclodextrin and sodium mercaptopropionate to obtain hepta-(6-S-(2-carboxyethyl)-6-sulfo)-gamma-cyclodextrin hepta-sodium salt. The method of the inventionis reasonable in design and mild in reaction condition, the prepared finished product is high in purity, and the method can achieve directional synthesis, meets the practical requirement of sugammadex sodium synthesis, and has wide market prospects.