Abstract: The method of residue analysis of a new sulfonylurea herbicide monosulfuron,its degradation in soil, and terminal residue in soil were studied. Residues of monosulfuron were extracted from soil with methanol ammonium hydroxide, followed by liquid liquid partition and cleaned up by C 18 column, concentrated to a small volume, and then determined by HPLC with UV detector. The average recoveries and coefficients of variation of the method were 95.10%～103.77% and 1.47%～11.80% respectively. The minimum detectable quantity of monosulfuron was 4 ng, the minimum detectable concentration of monosulfuron in soil sample was 0.02 mg/kg. The soil degradation of monosulfuron in Shandong and Beijing were determined with the method described above. The results showed that the field half lives of monosulfuron in the two kinds of soil were about 9.24 days and 13.59 days, respectively. When monosulfuron was applied according to recommended dosage, the final residues of monosulfuron in soils at the time of wheat harvest were not detected by this method.