Based on the modern statistical theory, the uncertainty sources of the analytical results of the determination of lead in tea by inductively coupled plasma mass spectrometry (ICP-MS) were analyzed. The uncertainty sources of the analytical results mainly include the weighing process, the constant volume process, the fitting of the standard curve in the instrument measurement, and the repeatability of the measurement process etc. The uncertainty components that affect the results of lead analysis in tea were evaluated by the methods of A and B, and the expanded uncertainty of 95% confidence probability was determined. The confidence interval of the analysis results was determined as [2.66, 2.86].