The invention discloses a preparation method of 3-hydroxybutyrate. The preparation method comprises the steps of adding esterase to an aqueous solution of ethyl 3-hydroxybutyrate for enzymolysis, filtering to obtain a filtrate, adding inorganic alkali for salifying, concentrating, crystallizing and conducting suction filtration to obtain the 3-hydroxybutyrate. The method has high yield. The prepared 3-hydroxybutyrate has good purity and low by-products, and the content of crotonate is less than 0.01%. The preparation method has simple operation and mild reaction conditions, and is suitable forindustrial production.