Galacto-oligosaccharides (GOS) is a natural functional food ingredient widely present in human breast milk. The production of GOS by β-Galactosidase is main commercial source. β-Galactosidase is a kind of important glycoside hydrolase， which has the ability to simultaneously catalyze the hydrolysis reaction and the transglycoside reaction. Due to the complexity of the source and application of β-Galactosidase， the corresponding GOS products are very different in structure and purity. Therefore， the research of β-galactosidase oriented to high-yield and high-purity GOS has been receiving extensive attention. This review compares the performance of β-Galactosidase in the process of catalyzing GOS from the perspectives of mechanism analysis， enzyme sources， and catalytic methods. On this basis， the research direction of β-Galactosidase in the production of GOS is prospected.