Objective: To establish an ultra-performance liquid chromatog.-tandem mass spectrometry (UPLC-MS/MS) method for the simultaneous determination of chlorate and perchlorate in infant formula milk powder. Methods: The sample is extracted, centrifuged, purified and filtered by a solid phase extraction column. After purification, the filtrate is measured in the neg. ion mode and quantified by the internal standard method. Results: Chlorate and perchlorate have a good linear relationship in the range of 2∼500 μg/kg and 1∼250 μg/kg resp. (R2>0.999), the detection limits are both 4.5 μg/kg, and the quantification limits are resp. 15, 7.5 μg/kg. For accuracy (n=9), the chlorate recovery rate was 90.4%∼104.3% at the three spike levels of 15.0, 30.0, 150 μg/kg, the three spikes at 7.5, 15, 75 μg/kg at the horizontal level, and the recovery rate of perchlorate is 80.2%∼106.2%. For method precision (n=7), the RSD of chlorate was 4.74% and the RSD of perchlorate was 8.31%. Conclusion: The linearity, precision and accuracy of this method meet the requirements of GB/T 27417-2017 "Guidelines for the Confirmation:and Verification of Chem. Anal. Methods", and it is suitable for the simultaneous anal. of chlorate and perchlorate in infant formula milk powder detection.