Abstract: In order to determinate the astragaloside in the astragalus by Semi-LC/MS, diosgenin is used as an internal standard compound, a chromatography guard column was used to remove most interference components and enrich the target compound which was subsequently determined by MS under multiple reaction monitoring (MRM) scanning-mode. The calibration curve is linear over the range of 2.85—57.0 mg/L of astragaloside. The RSDs for the stability and reproducibility experiments are less than 3%, and sample recovery rate is 98.9%. Semi-LC/MS is one simple, efficient, sensitive method for rapid quantitative analysis of astragaloside in astragalus samples.