The invention discloses a method for screening a sweetening agent in milk and dairy products by applying ultra-high performance liquid chromatography-quadrupole electrostatic field orbit ion trap mass spectrometry, and belongs to the technical field of food safety inspection. An optimized QuEChERS method is used for preprocessing samples; the ultra-high performance liquid chromatography-quadrupole electrostatic field orbit ion trap mass spectrometry is applied for performing screening, a scanning mode of full-scanning/data-dependency collection and full-scanning/variable data-independent collection and full-scanning/full-ion fragmentation collection is adopted, a positive ion or negative ion mode is selected for scanning, and complete first-order and second-order spectra are obtained; Extract Finder 2.5 software is applied for processing the obtained first-order and second-order spectra, and information of a compound is extracted. Information in a built spectrum library and a tested object screening result are compared, and the composition of the sweetening agent in the milk and dairy products is ensured. An adopted mass spectrometer has the main advantages that the resolution is high, qualitative and quantitative results are accurate, sensitivity is high, and quality precision is high and can be applied to complex matrix analysis. The established screening method has the good application prospect in the field of food.