A quantitative method was established for the determination of Δ9-tetrahydrocannabinol in cannabis using high performance liquid chromatography.Methanol was selected as the solvent to extract tetrahydrocannabinol from cannabis plant or resin.The separation of tetrahydrocannabinol was performed on a Shimadzu ODS-SP column(150 mm×4.6 mm,5 μm) using water-acetonitrile as mobile phase by gradient elution.The primary quantitative wavelength of UV detector was set at 210 nm and the auxiliary one was at 195 nm or 220 nm.Flow rate was set at 1 mL/min,column temperature was 40 ℃ and injection volume was 10 μL.Under the optimal conditions,good linearity was achieved over the range of 0.5-100.0 mg/L,with correlation coefficients(r2) more than 0.999 99.The limit of detection(S/N≥3.3) was 0.12 mg/L and the limit of quantitation(S/N≥10) was 0.40 mg/L.Using this method to detect a cannabis resin sample,the result of uncertainty evaluation on Δ9-tetrahydrocannabinol’s content was 5.32%±0.17% with k value of 2.The result showed that the method was rapid,sensitive and accurate,and was applicable in the quantitative determination of cannabis plant and resin.