Abstract: A alkyl-diol silica was synthesized by three steps：first，γ-Chloropropylsilane-substituting of silica, then esterifying of γ-Chloropropylsilane-substituted silica and last digesting of ester by lipase. Under 20MPa pressure, pre-column were packed with the material(35×4.6mm I.D). Efficient on-line clean-up and concentration atrazine and simazine was studied by the pre-column as the first column and an ODS column (250mm×4.6mm I.D) as the second column ( analytical column). Sample matrix are discharged by the pre-column. The mobile phases applied consisted of 0.1% HOAc (pH3.0) acetonitrile-water on extraction column with UV detection at 225nm. Then, coupled-column liquid chromatographic methods for the direct analysis of atrazine and simazine in urine was established. As a result, the system showed good chromatographic property in the on-line analysis of atrazine and simazine in urine.