Abstract: By the gas chromatographic method,the determination of ametryn degradation dynamics and final ametryn residues in pineapple and soil was conducted.The results show that its minimum detectable amount is 0.0232ng,its minimum detectable concentration is 0.002mg/kg in pineapple and 0.005mg/kg in soil,the average recoveries in pineapple and soil are 87.23%～92.10% and 88.80%～93.77%,respectively.When 80% ametryn was used at a dose of 4800g(a.i)/hm²,it had been found its initial residues in pineapple and soil are 0.1448～0.1646mg/kg and 3.3318～3.5536mg/kg,respectively and their half-lives are 29.17～29.45 days and 25.75～30.68 days,respectively.The final residues in the pineapple that received the treatment of ametryn for 1 time and with an interval of 10 days are 0.1646mg/kg and 0.1488mg/kg in 2 years.The amount of ametryn residues are lower than the maximum residue limit stipulated by EU(0.2mg/kg)