Abstract: FAAS, which is short for flame atomic absorption spectrometry, is a method widely used to assess Li₂O₃ content in vitrified bond.To improve the accuracy, comparative tests were implemented to study the uncertainty caused by test repeatability, linear regression of standard curve, liquid volume, dilution degree and sample weighing.The combined uncertainty and expanded uncertainty was calculated based on an international method.Resultsshow that test repeatability and linear regression of standard curve affect the uncertainty most.In conclusion, when determining the content, parallel repetitive measurement should be conducted with special attention paid to solution concentrations when drawing a standard curve.