Aiming at the difficulty in the determination of reverse flotation reagents in potash production,a method for the direct determination of trace dodecyl morpholine by gas chromatography-mass spectrometry was established.The sample was dissolved and then three times extracted by n-hexane.The instrument conditions were as follows: chromatographic column TG-5MS,Length：30 m,ID：1.9 μm,Film：0.25 μm.Mass spectrum parameters：EI source,IonTemp erature：240 ℃,Capillary Temp：250 ℃.Sample Size：1 μL,Flow Velocity：1 mL/min and diffluence ratio was 40:1.Chromatographic column temperature was programmed temperature.The standard working curve was of good linearity,and the precision and recovery rate met the requirements of the analysis.The relative standard deviation was ≤2%.The detection limit of the method was 0.15 g/mL,and the limit of quantification was 0.5 g/mL.