Provided are a beta-galactosidase GalA and the use thereof. The amino acid sequence of the beta-galactosidase GalA is shown as SEQ ID NO. 1. Further provided are a recombinant expression of the beta-galactosidase GalA, and a method for preparing and purifying same. The enzyme activity of the fermentation liquor can reach 3795.6 U/mL, the purity after one-step purification is more than 97%, and the recovery rate is 79.5%. The beta-galactosidase GalA has good thermal stability and storage stability, and the optimal reaction temperature is 50°C. 89.7% of enzyme activity is still retained after continuous incubation for 24 h at 50°C, and 81.5% of enzyme activity can still be retained after storage for 30 days at room temperature (30°C). The beta-galactosidase GalA has a high activity, a good stability, and a strong ability to degrade lactose, and has a good application potential.