Abstract: The urine sample was extracted with Waters Oasis HLB LP column, and the column was eluted by acetonitrile. HPLC-MS/MS was applied to the determination of simazine in the eluate. Eclipse Plus C₁₈ chromatographic column was used as stationary phase, and 70% (volume fraction) acetonitrile solution was used as mobile phase. ESI⁺ and multi-reactions monitor mode were adopted in MS/MS. Linear relationship between values of peak area and mass concentration of simazine was kept in the range within 500.0 μg·L^-1, with detection limit (3s/k) of 0.91 μg·L^-1 and lower limit of determination (10s/k) of 3.03 μg·L^-1. On the base of blank sample, test for recovery was made by standard addition method; values of recovery found were in the range of 80.7%-84.0%, with intra-day RSDs (n=6) and inter-day RSDs (n=4) of determined values in the ranges of 1.8%-2.9% and 6.8%-9.1%, respectively.