Abstract: A determination method of three kinds of triazine pesticides(Atrazine, Cyromazine and Metolachlor) residue in milk and dairy products by isotope dilution-high performance liquid chromatography-high resolution mass spectrometry was established. The samples were extracted by acetonitrile and purified by C₁₈ solid phase extraction column. The mobile phase program was gradient elution with 0.1% formic acid aqueous solution. The samples were separated by Hypersil Gold C₁₈ column. Electrospray positive ions (HESI⁺) and full MS/dd-MS² mode were used for qualitative and quantitative detection. The results showed that the linearities relationship were good in the range of 1.0~50.0 ng/mL (R²≥0.99). The detection limits of this method were 5 μg/kg, and the average recoveries were 81.6%~104.0% and the relative standard deviations were 0.55%~4.14% with levers of 5, 10 and 25 μg/kg. The method is suitable for the determination of three kinds of triazine pesticides residues in milk and dairy products, with high sensitivity, good reproducibility and reliable results. It provides technical support for ensuring the food safety of milk and dairy products in China.