Objective:Objective:Evaluating the uncertainty of the determination of aerobic bacteria in the formula granules of Radix Polygoni Multiflori Preparata.Methods:The total number of aerobic bacteria in Radix Polygoni Multiflori Preparata formula granules was determined by using the four non-sterile product microbial limit inspection method of the Chinese Pharmacopoeia 2020 edition.Through establishment of the math. model, identifying and analyzing the sources of uncertainty, quantifying each componens, and synthesizing the relative standard uncertainty and expanded uncertainty of measurement results.Results:The expanded uncertainty is U= 0.0826 log10(cfu/g), the interval of numerical value is(2.4426±0.0826)log10(cfu/g), and the interval of neg. number is(230, 340)cfu/g, k=2.Conclusion:The contribution of uncertainty introduced by electronic balance is small, The uncertainty caused by the preparation of test solution, diluent sample addition and repeatability experiment contributed a lot.