Abstract: An flow circuit of HPLC analysis,consisting of the driving system(bi-pump and single value system) and the column switching system(pretreatment column and analytical column) was designed and applied to the determination of anillicit additive,ribavirin,in antiviral oral liquor.The oral liquor sample was centrifuged and diluted with 0.3 g·L-1 NaH2PO4 solution to a definite volume.A aliquot of the sample was introduced into the pretreatment C18 column(mode A of the flow circuit),where the purification process was performed.Mobile phase consisting of CH3OH and H2O,in the ratio of 1+3,was used in the pretreatment column.Drug components adsorbed on the pretreatment column was eluted directly into the analytical kromasil C18 column(250 mm×4.6 mm,5 μm) with 0.3 g·L-1 NaH2PO4 solution as mobile phase by switching to mode B of the flow circuit,and ribavirin was determined with UV-detector at 205.6 nm.Linearity range was found in the range of 0.4-40.0 mg·L-1,with a detection limit(S/N=3) of 0.08 mg·L-1.Test for recovery was made at 3 different concentration levels of 1.0,5.0 and 10.0 mg·L-1 of ribavirin,giving average values of recovery(n=5) 98.32%,98.45% and 99.45% respectively.