To establish a method for quercetin content determination of the three plant drugs from genus Sedum and to decide their best harvesting time. Dried herbs of Sedum sarmentosum Bunge., S. lineare Thunb. and S. erythrostictum Migo. are all traditional medicines from Genus Sedum. They all have long been used to cure hepatitis, dysentery, swelling poison and so on. It has been reported that flavonoids contained in S. sarmentosum Bunge. were one type of the active components to protect liver and reduce serum alanine aminotransferase level. Through the qualitative analysis and TLC assay, we have verified that both S. lineare Thunb. and S. sarmentosum Bunge. contain flavonoid glycosides whose aglycones include quercetin. In this study, a HPLC methodology was established to determine quercetin which was a common hydrolyzate of the flalvonoid glycosides in the three plant medicines. The determination method developed showed good linearity in the range of 41.2-412.0 μg/mL, and had a nice accuracy and repeatability. It indicated that the content of quercetine in Sedum sarmentosum, Sedum lineare and Sedum emarginatum can achieve the quality standard required by Chinese Pharmacopoeia.( No less than 0.01%), The results also revealed preliminarily a relation between collected season and medicine quality. Thus it could be used to control some flavonoids content in the three plant drugs indirectly. By determining the samples of the 3 drugs collected in different seasons, the optimal harvest periods could be preliminarily ascertained.