Objective:To establish the method of dete rmining the quantity of hypericin in Hypericum perforatum and determine the quantity of the hypericin in defferent medicinal materials and asepsis seedings which grow in defferent environment. Method: The specime n is extracted with methanol --Pyridine (9∶1)ultrasound extraction. Chromat ographic assay is performed on a hypersily ODS 2(4.6 mm×150 mm,5 μm)colum. The mobile phase is composed of methanol -1.56% dihydric natrium phosphate hydrogen natrium solution (shift solution's acidity to 2.1 with phosphoric ac id )--ethyl acetate (4∶1.9∶1), velocity of flow is 1 mL·min -1 ; co lum temperature is 35 ℃;the detection wavelength is 590 nm. Result : A satisfactory seperaration between hypericin and impurity. The ca libration curve is linear over the range of 0.052 4～0.262 0 μg for hypericin( r=0.999 8). The average recovery of hypericin is 97.50%. Conclu sion: The quantity of hypericin in Hypericum perforatum has som ethi ng to do with the genetic factor , environment factor, growing period and dry me ans. The method of determining the quantity of hypericin can be regarded as the method of controling the quantity of medicinal materials.