Abstract: A rapid method is applied to analyze the ethanol extract of the roots of baishan aconitum plants by electrospray ionization-tandem mass spectrometry (ESI-MS 2). The information of molecular weight and the furthermore information of structure are obtained from the complex system by ESI-MS 2. 9 kinds of aconitum alkaloids including hypaconitine, mesaconitine and aconitine, the hydrolysis products of mesaconitine and lipo-alkaloids were found.