Abstract: The residues and fate of ¹⁴C-metalaxyl in soil-tobacco system were studied in simulated field condition. The results showed that metalaxyl could move in soil layer, and mainly affected by the movement of water. The half life was 2～3 weeks for extractable residues, and 5 weeks for total residues in soil. The percentage of bound residues in total residues increased by the time. after 6 weeks it reached to 23.1%. Tobacco could absorb and accumulate metalaxyl by roots. The concentration of extractable residues in tobacco began to reduce from the second week,and its half life was 1～2 weeks. After six weeks, the concentration of extractable residues reduced to 5.35 mg/kg. One metabolite was found in methanol extracts. The behavior of methonal extractable residues in soil-tobacco system could be described by two compartments dynamic model.