Objective An analytical method was established to determine seven organophosphate esters （OPEs） flame retardant residues in milk by ultra-high-performance liquid chromatography-high-resolution mass spectrometry.Methods Samples were extracted， cleaned up， and enriched using an acetonitrile-water cold-induced liquid-liquid extraction （CI-LLE） technique. The chromatographic separation of OPEs was performed on an HSS T3 column （2.1 mm × 100 mm， 1.8 μm） by gradient elution using methanol-water as mobile phases. The analytes were detected by high-resolution mass spectrometry using targeted single-ion monitoring mode， and the internal standard method was used for quantitative analysis.Results The determination of seven OPEs showed a good linear relationship ranging from 0.2 to 20 μg/L （R² >0.99）. The limits of detection and quantitation were in the ranges of 0.01-0.21 μg/L and 0.04-1.72 μg/L， respectively. At three different spiked levels， the recoveries for pesticides in blank samples ranged from 88.4% to 118%， with relative standard deviation of 1.15-7.15%.Conclusion This method is simple， reproducible， and sensitive and can be applied to determine trace OPEs in milk.