Objective： This study aimed to evaluate the safety of pesticide residues in liquid milk. Methods： A method for simultaneous determination of 11 kinds of pesticide residues by ultra-high-performance liquid chromatography-tandem mass spectrometry was established. The samples were extracted by acetonitrile, purified by C₁₈ and PSA solid phase extractants, separated on a column Xbridge BEH C₁₈ (100 mm×2.1 mm, 1.7 μm), determined in multi-reaction monitoring mode, and optimized for pre-treatment parameters using response surface method. Results： The optimal conditions for pretreatment were 10 mL acetonitrile, 50 mg C₁₈ and 30 mg PSA. The linear relationships of 11 kinds of pesticides were good in the concentration range of 1.0~100.0 μg/L, and the correlation coefficients (R²) were all > 0.999. With addition of 10, 20, 100 μg/kg, the average recoveries were 82.7%～102.0%, the relative standard deviations were 2.89% to 8.87%, and the limits of detection (LOD) and limits of quantitation (LOQ) were 2.0～3.0 μg/kg and 5.0～10.0 μg/kg, respectively. Conclusion： The method is simple, convenient, rapid, high recovery rate and high reproducibility, which could accurately determine 11 kinds of pesticide residues in liquid milk.