Abstract: Identification of the flavonoids from natural plant of Apocynum venetum leaves with HPLC-ESI-MS was established. The compositions of its extract were detected by the high-performance liquid chromatography, and eight chromatography peaks obviously were tested. Then the sample of crude extract was measured by HPLC-ESI-MS, eight compounds was examined. The characteristic ions and fragment reaction were analyzed. HPLC-ESI-MS was a rapid and effective method for identifying compounds from natural plant.