To establish a liquid chromatography coupled with tandem mass spectrometry(LC-MS/MS) method for simultaneous determination of aconitine，hypaconitine and benzoylaconitine in rat plasma，and to study the pharmacokinetics of the three components in rats after administration of Radix Aconiti Kusnezoffii Praeparata.Methods:Berberine was used as internal standard，and chromatographic separation was performed on a Shim-pack Velox SP-C18(100×2.1 mm，2.7 μm) with water-methanol-acetonitrile(0.05% formic acid) as the mobile phase at the flow rate of 0.3 mL/min.The mass spectrometry was carried out by electrospray ionization(ESI)，positive ion mode and multiple reaction monitoring(MRM).The plasma samples were precipitated by organic reagent.Results:The linear relationship of aconitine，hypaconitine and benzoylaconitine was good(r≥0.999 0).The intra-day and inter-day precision met the requirements of biological sample analysis，with RSD less than 15%.Conclusion:This method is highly sensitive and specific，and it is suitable for the determination of aconitine，hypaconitine and benzoylaconitine and the study of the pharmacokinetics.