Abstract: The uncertainty for determination of selenium content in selenium-rich eggs by atomic fluorescence spectrometry was analyzed.A mathematical model in the process of measurement was established combining the test method.The uncertainty sources for each parameter in the model were analyzed.And that the problems in the process of evaluating uncertainty should be paid attention to was also discussed. Based on the analysis of uncertainty, the sample concentration from the standard curves and repeatability experiments were the major sources of uncertainty, while sample weighing revealed little effect on the final uncertainty. The expanded uncertainty of selenium in selenium-rich eggs was determined with this method, and the final result was expressed as: ( 0.2705 ± 0.0082) mg /kg (k = 2) .