Abstract: An analytical method was developed for determination of chlormequat residues in soil.Chlormequat was extracted from the matrices by methanol-ammonium acetate solution and then analyzed by reversed phase HPLC with electrospray mass spectrometric detection.Mass spectral acquisition was realized by select ion monitoring of chlormequat cation.The limit of detection (LOD) was 0.01 mg/kg,and the limit of quantitation (LOQ) was 0.05 mg/kg.The linear range is 0.01 ~1.0 mg/kg and the correlation coefficient (r2) was more than 0.996.The average recoveries ranged from 75.1% to 87.2% for chlormequat in replicate sets of soil samples fortified with standard concentration of 0.05,0.5 and 1.0 mg/kg,and the relative standard deviation (RSD) were less than 10%.With the established method,the dissipation rate of chlormequat in soil was studied,showing a half-life of 4.47 d.