The endocrine disrupter simazine was oxidized by O3/H2O2 and the reactive productions was analyzed by chromatography to assess the degradation efficiency of Simazine. The initial content of Simazine 2 mg/L was removed about 87.1% by O3H2O2 system when the O3 was dosed as 10.0 mg/L, the H2O2/O3 molar ratio was 0.70, the temperature was 26 degrees C and pH 7-8, which indicated Simazine could be conveniently removed by O3/H2O2 system in ordinary reactive condition. The simazine removal ratio in tap water was 10% more than it in purified water up to 86.9%. The removal of simazine was decreased when the content of humic acid (HA) was high, whereas it was increased while low content HA in water. Also, the removal efficiency was inhabited by hydrogen carbonate fairly. The deethyl-simazine (DES) was trapped by Gas Chromatography Mass Spectrum(GC-MS) which was also certificated by analyzing the Liquid Chromatography Mass Spectrum (LC-MS) of the products. The Ion Chromatography spectrum showed the existing of de-chloro-procedure and breakage of triazine ring. Which indicated the oxidizability of O3/H2O2 system was fairly strong.