Objective To enhance the level and ability of measuring pesticide residues in raw milk and find out the primary factors of affecting measurement uncertainty.Methods The mathematic model of measurement was established in order to evaluate measurement uncertainty of organophosphorus pesticide residues in raw milk with gas chromatography.Results The standard measurement uncertainty of organophosphorus pesticide residues in raw milk made up of weighing,sampling and diluting procedures,standard matter,sample volume,instrument calibration.The calculating formula of expanded measurement uncertainty was U=k?CX?urel(tptal).The expression of measurement result was C=CX?U.Volume of 6 kinds of organophosphorus pesticides residues were 0.4?0.050,0.4?0.029,0.4?0.027,0.4?0.029,0.4?0.057,0.4?0.034(mg/kg) respectively in raw milk which the standard matter of pesticide was added in.Conclusion From the evaluation of measurement uncertainty of pesticide residues in raw milk with gas chromatography,we can see that the measurement uncertainty is composed of many factors,which commonly comes from random variable and fuzzification,and can be assessed by statistic distribution and standard deviation.