Elimination of herbicide residues in agricultural production plays a key role in the sustainable development of modern agriculture in China.In order to discover and isolate more efficient sulfonylurea herbicides-degrading microbes，and study the pathway of chlorimuron-ethyl biodegradation，chlorimuron-ethyl was used as the sole nitrogen source for the isolation of efficient chlorimuron-ethyl degrading bacteria LAM2021 from sludge sample collected from a sulfonylurea herbicides manufacturer.Based on the physiological and biochemical characteristics，and phylogenetic analysis of 16S rRNA gene sequences，the strain was considered to be a member of the genus Kosakonia(Kosakonia sp.).The best degradation condition of strain LAM2021 on 50 mg/L chlorimuron-ethyl optimized by RSM from the results obtained from single factor experiment was under 30℃，at pH 6.0 with 5% inoculum，94.6% of 50 mg/L chlorimuron-ethyl will be degraded in 11 h under the optimum condition.The acids generated during the degradation of chlorimuron-ethyl by strain LAM2021 in the mineral medium with glucose were detected and identified by high performance liquid chromatography(HPLC)，citric acid was found to be the predominant one.The degradation mechanism was deduced based on the intermediates and acids production during the degradation process:strain LAM2021 metabolited the glucose into citric acid when its growth was stressed by the chlorimuron-ethyl，then the sulfonylurea bridge was broken under an acidic condition with the accumulation of generated citric acid.Through the analysis of the whole genome sequence of strain LAM2021，esterase genes that may contribute to the degradation of chlorimuron-ethyl were predicted.Five intermediates formed during chlorimuron-ethyl degradation by strain LAM2021 were detected by liquid chromatography mass spectrometry(LC-MS).According to the chemical structure of chlorflusulfuron and the characteristics of its intermediate metabolites，it is speculated that the metabolic pathway of strain LAM2021 to degrade chlorimuron-ethyl is:the urea bridge in chlorimuron-ethyl was broken into 2-amino-4-chloro-6-methylpyrimidine，and ethyl formate benzene sulfonamide，then the ester bond was de-ester to ethyl phthalate benzene sulfonamide，and finally cyclized to N-aldehyde saccharin.