A liquid chromatography－tandem mass spectrometry（LC－MS/MS） was established for the simultaneous determination of thiencarbazone-methyl and its metabolites including BYH18636-carboxylic acid（M01），BYH18636-sulfonamide-carboxylic acid（M03），BYH18636-sulfonamide（M15） in water，soil and sediments．Water samples were firstly acidated by formic acid，then extracted with HLB solid phase extraction（SPE） cartridge，while the soil and sediments samples were firstly extracted with acidated acetonitrile and cleaned up with primary secondary amine（PSA） cartridge，then detected by LC－MS/MS．The separation was carried out on an Agilent Poroshell 120EC－C,18,（2.1 mm × 75 mm，2.7 μm） column by gradient elution with acetonitrile and water as the mobile phases．The detection was carried out with electrospray ion source in negative ion mode under multi-reaction monitoring（MRM） mode．External standard method was applied to obtain the matrix-matched calibration curve for quantification．Results showed that there were good linear relationships for thiencarbazone-methyl and its metabolites in the range of 0.001－0.1 mg/L，with their correlation coefficients（,r,2,） more than 0.995．The average recoveries for water samples at three spiked levels of 0.1，1 and 10 µg/L ranged from 75.5% to 104%，with relative standard deviations（RSDs，,n ,= 5） of 1.4%－8.6%，while the recoveries for soil and sediment samples at three spiked levels of 0.5，5 and 50 µg/kg ranged from 75.4% to 105%，with RSDs of 1.5%－9.7%．The quantification limit of four analytes was 0.1 µg/L in water，while 0.5 µg/kg in soil and sediments．With high sensitivity，accuracy and good repeatability，this method is suitable for the simultaneous determination of thiencarbazone-methyl and its metabolites in water，soil and sediments.