Abstract: The measurement uncertainty of the analytical results of Ag in groundwater samples by inductively coupled plasma-mass spectrometry (ICP-MS) was evaluated using continuous propagation model of uncertainty. The regression of double error was used in the course of standard curve fitting. The extended uncertainty of measurement results was obtained from the synthesis of uncertainties from each source. When the silver content of the actual samples is relatively low, the uncertainty generated in the course of standard curve fitting is comparatively large and even becomes the dominant factor.