Abstract: Evaluation of uncertainty in measurement for the method of HG-AFS determination of mercury in water was described in this paper.It was considered that in the whole process of analysis,the courses of preparation of standard solutions,preparation of calibration curve and analysis of the sample were three main sources of uncertainty.Based on this recognization,mathematical models were constructed and each of the variables in the equation was analyzed and its uncertainty evaluated.Combined uncertainty and expanded uncertainty were calculated statistically.