Abstract：Field trail for S-metolachlor residue in sunflower and soil were conducted in Beijing and Jilin province，respectively.The results showed that the half-1ife of degradation for S-metolachlor was 5.10d in plant of sunflower, 9.83d in soil in Beijing. The half-life of degradation for S-metolachlor in Jilin was 11.89 d in plant of sunflower，7.21 d in soil．Two-year and two-area results showed that the terminal residues in sunflower field samples were lower than MRL(0.1 mg/kg). When S-metolachlor was applied to the sunflower seed field ecosystem at the recommended dosaged, the sunflower harvested coule be sonsidered safe.