Abstract: After the mathematical model set up,the different parts of uncertainty analyzed,the combined standard uncertainty calculated and the evaluation of the uncertainty of analytical method observed,an evaluation method for the uncertainty of coumarin and safrole in food additives by gas chromatography-mass spectrometry was obtained.It has shown that the uncertainty of the repeatability is largest factor contributed to combined uncertainty.The expanded uncertainty of coumarin is shown as (1.52±0.098) mg/mL(k=2).The expanded uncertainty of safrole is shown as (1.33±0.082) mg/mL(k=2)on this method.