Abstract: In order to evaluate the environmental behavior of bromacil in pineapple, and provide the date of the MRL of bromacil in pineapple in China. Residue dynamics of bromacil in pineapple and soil was studied by field trial, and made qualitative and quantitative analysis by UPLC- MS/MS. In order to optimize the experimental conditions, the effects of different clenaning conditions (extraction solvent, SPE, elution solvent, elution volume) were investigated. The limit of detection was estimated to be 1×10^-12 g. The minimum concentration of detection in pineapple and soil was 5×10^-3 mg/L. The average recoveries of bromacil in pineapple and soil were 85.1%-86.5%, 84.0%-85.5% with relative standard deviation were 3.46%-6.78%, 2.74%-4.54%，respectively when the fortified concentration was 0.01-1 mg/L. It was fitted for the demand of pesticide residue analysis and detection. The trial results showed that the dissipation of bromacil in soil was in conformity with the first- order dynamic equation, the half- lives were 8.2- 11.1 days in soil. The terminal residues of bromacil in the whole fruits and flesh were＜0.01-0.01 mg/kg and＜0.01 mg/kg, respectively when the pineapple was sprayed once to twice according to the recommended dosage 4800 g/hm². The terminal residues of bromacil were all below the MRLs of Japan (0.05 mg/kg) and Austiralian (0.04 mg/kg) at harvest time.