Objective To develop a method of quantitative analysis of multi-components by single marker（QAMS） for simultaneously determining kaempferol-3-O-glucorhamnoside， astragalin and kaempferol in Thesium. Methods The chromatographic separation was achieved on C18 chromatographic column（phenomenex， 250×4.6mm， 5μm）， the mobile phase was methanol -0.4% phosphoric acid aqueous solution with gradient elution（0→5→10→20→45min， 45%→50%→55%→60% methanol）. The wavelength was 365nm. The flow rate was 1. 0 mL/min and the column temperature was 40℃. Kaempferol was used as the reference， the calibration factor of kaempferol-3-O-glucorhamnoside and Astragalin to that of kaempferol were calculated. And the contents of active constituents were calculated by the relative calibration factor to realize QAMS. At the same time， external standard method was used to detect the contents of the three constituents， the two methods were compared to validate the accuracy and feasibility of the new method. Results No significant differences were found in the quantitative results between the measured value and the calculated value. Conclusion The QAMS is feasible and accurate to evaluate the contents of the three active constituents in Thesium.