Abstract: The extraction and detection method of flavonoids in the leaf-used sweet potatoes was established by using the QuEChERS combined with UPLC MS/MS. By taking Fucaishu 18 as the material, and selecting the seven flavonoids including rutinum, isoquercitrin, taxifolin, quercitrin, quercetin, naringenin and kaempferol, the conditions such as the flow phase, mass spectrometry conditions, and purifying agent were determined in the experiment, so as to determine the extraction and detection method of flavonoids in the leaf-used sweet potatoes. The results showed that with 0.2 g C18 as the purifying agent and 0.1% formic acid water (A)- acetonitrile (B) as the flow phase, the collision energies of rutinum, isoquercitrin, taxifolin, quercitrin, quercetin, naringenin and kaempferol were -23/-40, 44/27, 23/32, 27/42, -31/-29, 25/24 and -33/-31, respectively. The seven flavonoids were completely separated within 5 min with good linearity in the range of 0.05-1 μg·mL^-1 (R² > 0.99). The recoveries of rutinum, isoquercitrin, taxifolin, quercitrin, quercetin, naringenin and kaempferol were 96.52%-97.64%, 97.26%-98.74%, 92.95%-94.62%, 96.23%-97.65%, 90.23%-92.56%, 99.12%-101.56%, and 83.65%-84.64%, respectively. In the matrix effect analysis, rutinum and isoquercitrin ME ranged from 100% to 120%, which showed the weak matrix enhancing effect and could be ignored. Quercetin and kaempferol ME ranged from 120% to 150%, showing the moderate matrix enhancing effect. Taxifolin ME was more than 150%, showing the strong matrix enhancing effect, while quercitrin and naringenin ME were both lower than 50%, showing the strong matrix inhibition effect. The seven flavonoids in Fucaishu 18 were detected, and it was found that Fucaishu 18 did not contain taxifolin, and the content of isoquercitrin in it was the highest, followed by rutinum. The method had strong specificity, high sensitivity and good reproducibility, which could provide reference for the extraction and detection of flavonoids in the leaf-used sweet potatoes.