Abstract: The residues change of chlorpyrifos and its toxic metabolite 3,5,6-trichloro-2-pyridinol in cucumber samples during each pickling process was determined by ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS).Results showed that the level of chlorpyrifos in cucumber after washing reduced 34%.After the primary and secondary pickling process,the residues of chlorpyrifos obviously rose to the level before washing with the total processing factor of the three processing steps at 0.97.The impact of washing process to the residue of TCP was not significant (only reduced 2.6%),while the residue of TCP was significantly increased after the primary and secondary pickling process with the total processing factor of the three processing steps at 1.63.The result indicated that the level of chlorpyrifos has no obvious change in cucumber after pickling process,while the residue of its toxic metabolite TCP was obviously increased.