［［Objective ］］ To evaluation the uncertainty of determination of methamidophos residues in vegetable oil by ultra -performance liquid chromatography -tandem mass spectrometry.［［Methods ］］ A vegetable oil sample was detected by ultra -high performance liquid chromatography -tandem mass spectrometry,and the recovery rate was determined at the same time.By analyzing the sources of uncertainty in the experimental process,the measurement uncertainty was ultimately evaluated.［［Results］］ The residue amount of methamidophos in olive oil samples was not detected,and the uncertainty of the accuracy 1 sample was evaluated,The results were （0.018±0.010） mg/kg.［［Conclusion ］］ In the uncertainty measurement process of methamidophos residue in vegetable oil,the influence of standard curve fitting,ultra -high liquid chromatography -mass spectrometry,and standard working solution is relatively large,while the influence of sample weighing,sample pretreatment,and sample repeatability determination is relatively small.