Abstract:A measurement model was established，the independent uncertainty，standard uncertainty and expanded uncertainty coming from analysis procedure were obtained.The major source of the uncertainty was the calibration curve calculated on the basis of the principle of method of least squares when determining C.As selenium content in milk powder for infant and young children was 0.310 mg/kg，the expanded uncertainty was 0.046 mg/kg and the coverage factor k was 2.This method was suitable for evaluating the uncertainties in the measurement of selenium in milk powder for infant and young children.