The tender shoots of Chinese toon are one of the most popular vegetables, although the chemical basis of its edible value is still unknown. Guided by antioxidant and α-glucosidase inhibitory activities, the main constituents and their function and content in Chinese toon buds were studied. Six main flavonoid glycosides based on quercetin (1–3) and kaempferol (4–6), kaempferol (7), and a methyl gallate (8) with antioxidant and α-glucosidase inhibition activities were isolated and identified using chromatographic and spectrometric techniques and methods. The contents of the seven main flavonoids determined by high-performance liquid chromatography method were ranged from 0.5 to 5.1 mg/g, and the total flavonoids content measured by ultraviolet spectrophotometry was 17.1 mg rutin equivalent/g dry weight, which was higher than that found in 11 other common vegetables. Correlating the activities and contents of these flavonoids, Chinese toon bud is a potentially rich source of dietary antioxidants and hypoglycemics.