A method for the simultaneous determination of residue of pretilachlor and simetryn in rice filed environment by ultra-performance liquid chromatography tandem mass-spectrometry (UPLC-MS/MS) was established. The residues in unpolished rice, rice husk, plant, soil and field water were extracted by acetonitrile, purified by N-propyl ethylenediamine. The residues of pretilachlor and simetryn in samples were determined by UPLC-MS/MS. Pretilachlor showed a good linear relationship in the range of 0.01～ 5.0mg/L with the correlation coefficient of 0.9974 and the average recovery rates in unpolished rice, rice shell, plant, soil and field water were 71.8%～103.6%; Simetryn showed a good linear relationship in the range of 0.005～2.5mg/L with the correlation coefficient of 0.9979, and the average recovery rates in different samples were 75.0%～107.3% with their relative standard deviations of 1.7%～9.2%. The method has good repeatability, accuracy and precision, and can meet the technical requirements.