Abstract: A glycoside hydrolase, relating to the technical field of enzyme engineering/gene engineering. Provided are an enzyme of a GH112 glycoside hydrolase family, and an application of synthesizing human milk oligosaccharides (HMOs) by using an enzyme of a GH112 glycoside hydrolase family. A synthesis reaction is catalyzed by using the enzyme of the glycoside hydrolase family 112 (GH112) that is classified according to a Carbohydrate-Active-Enzymes (CAZy) database (http://www.cazy.org); and lacto-N-tetraose (LNT) is generated in an aqueous solution comprising lactose and/or galactose and/or galactose-1-phosphate and lacto-N-triose (LNTII). The enzyme of the glycoside hydrolase family 112 (GH112), and the preparation method therefor and the application thereof provided by the present invention have economic and social values.