Disclosed is a method of mass producing potato seedlings, comprising collecting growing points of seed potatoes and culturing the growing points in a liquid or solid medium; introducing in vitro plantlets obtained from the culture of the growing points to solid culture; and removing the in vitro plantlets from the solid culture, and planting through stem cutting and acclimatizing the in vitro plantlets in deep flow culture, in which a nutrient solution is circulating. When in vitro-cultured plantlets are planted in DSCAC through stem cutting, and sprouts from the terminal and lateral buds of the plantlets are hardened by gradually increasing light levels from the dark condition, the plantlets have healthy dark-green leaves and a high accumulation of carbohydrates, thereby obtaining potato seedlings having long stems that appear robust but not overgrown, and elastic and short nodes. Upon planting in hydroponic facilities, such potato seedlings have high adaptability to the external environment and thus rapidly, uniformly generate roots in a short time. The rapid root anchoring prevents planted seedlings from withering, leading to death, growing poorly, and the like. The direct planting of in vitro plantlets through stem cutting without a separate acclimatization process shortens the overall production period of potato seedlings by omitting the acclimatization process.