To determine the uncertainty of determination of sulfur dioxide in Northeast black fungus by distillationlead acetate absorption titration, this paper had made a great effort. According to GB 5009.34-2016 food sulfur dioxide determination, JJF 1059.1-2012 measurement uncertainty evaluation and representation and CNAS-GL006:2018 chemical analysis uncertainty assessment guideline, the mathematical model of sulfur dioxide uncertainty evaluation was established. The uncertainty introduced in the determination process of sulfur dioxide is classified and quantified, and the standard uncertainty and relative uncertainty components of each uncertainty component are calculated separately. The relative standard uncertainty of sulfur dioxide content in Northeast black fungus was 0.038 g/kg, and the residual sulfur dioxide content was（3.10±0.038） g/kg. The uncertainty of sulfur dioxide content in black fungus is mainly introduced by the concentration of iodine standard solution and the volume of iodine standard solution actually consumed by titration. Besides, it is introduced by the repeatability of sample measurement.More attention should be paid during the period of experiment, so as to improve the accuracy of the experiment data.