Abstract: According to the national standard method for determination of fluosilicic acid in anhydrous hydrogen fluoride， combined with daily measurement results，uncertainty of determination results of fluosilicic acid in anhydrous hydrogen fluoride was evaluated.According to the relevant provisions of Evaluation and Expression of Uncertainty in Measurement （JJF1059—1999），the mathematical model of uncertainty evaluation was established，and several major error sources， including the balance error，spectrophotometer′s standard curve error，and measurement repeatability of uncertainty etc.， were discussed.By calculating the component uncertainties，the expanded uncertainty was obtained by composing.In accordance with assessment results，it was found that measurement repeatability was the major influencing factor for the uncertainty.

Key words: anhydrous hydrogen fluoride, fluosilicic acid, uncertainty