Taking the polyethylene resin for food packaging as an example, the determination of ignition residue of polyethylene resin was measured, the mathematical model was established and the impacts of sources of measurement uncertainty were analyzed and evaluated such as measurement repeatability, the weighing process and result data rounding according to GB31604.6—2016 “National Food Safety Standard Determination of Ignition Residues in Food Contact Materials and Products”. The evaluation results showed that the measurement uncertainty of ignition residue mainly came from the maximum tolerance of electronic scales and the requirement of constant weight. With the same coverage probability, the higher the precision of the electronic scale was, the smaller the measurement uncertainty would be, and the higher the constant weight requirement was, the smaller the uncertainty would be correspondingly. The result data rounding should be reasonable owing to its impact on the measurement uncertainty. Repeatability also exerted a certain proportion of the impact on the measurement uncertainty to avoid human error and reduce measurement uncertainty to a certain extent through increasing the number of measurements.