The alpha-galactosidases, which can catalyze the removal of alpha-1,6-linked terminal galactose residues from galactooligosaccharide materials, have good potential for industrial applications. The high-level and efficient secretion of the alpha-galactosidases into the extracellular space has greatly simplified the downstream bioengineering process, facilitating their bioapplications. In this study, the effects of gene dosage and endoplasmic reticulum secretion-associated factors (ERSAs) on the secretory expression of an alpha-galactosidase gene derived from a Aspergillus oryzae strain were investigated by constructing multicopy expression cassettes and coexpressing the alpha-galactosidase gene with ERSAs. With the increase in the gene copy-number in the host genome, the expression of GalA was improved. However, the secretory expression level was not linearly related to the copy number. When the number was higher than four copies, the expression level of GalA gene declined. The ERSAs factors HAC1, PDI, and Ero1 improved the secretory expression of alpha-galactosidase, while Hsp40 inhibited its secretion. After methanol-induced expression in a bench-top bioreactor, Pichia recombinants carrying four copies of GalA genes reached 3520 U/mL in the supernatant of the culture. We further optimized the parameters for alpha-galactosidase to hydrolyze two types of galactooligosaccharides: raffinose and stachyose. This study has fulfilled the scale-up production of alpha-galactosidase, thus facilitating its industrial applications.