Abstract: The content of astragaloside Ⅳ in Astragalus essence was determined by HPLC-ELSD.The chromatography column was Agilent C18（5 μm,4.6 mm×250 mm）;the column temperature was 35 ℃;the mobile phase was acetonitrile and water（34：66）;the flow rate was 1.0 mL/min;the temperature of drift tube of ELSD detector was 65 ℃,and the air pressure was 30 psi.Results showed that the astragaloside Ⅳ within 32.12-321.20 μg had good linear relationship（r=0.999 8）;average recovery was 99.26%,and the RSD was 2.75%（n=6）.It is suggested that the method is simple and accurate and has good reproducibility,so it could be used in quality control method of Astragalus essence.