The objective  is to  determine   the  mass  concentration   of  nitrate   nitrogen    from   water      in      Hangzliou Bay by ionchromatography and  analyze its results uncertainty.  The        uncertainty  model  was establislied   for  determining nitrate     ni­trogen mass  concentration from water   sample  by ion   chromatography,  and the  uncertainty   sources were  also  analyzed.The measurement uncertainty was mainly due to 4 aspects，including the preparation of standard solution，the standard curve fitting, the repeated measurements and the injection volume. The uncertainties of t!ie standard curve fitting and repeated measurement  accounted for about 42%   and 47%，of  the  total  uncertainties，respectively.   The nitrate nitro­gen content from water sample in HangzJiou Bay was 1. 36 mg/L and its expanded uncertainty was 0. 13 mg/L. So the nitrate nitrogen content in the water sample was % 1. &6 ± 0. 1& ) mg/L. It was concluded that the method established for t!ie  uncertainty   analysis and calculation  can be used   for the uncertainty  evaluation for   determining  nitrate  nitrogenof water sample by ion chromatography method. ' Chinese Fishery Quality and Standards，2015，5 % 3 ):40 - 46 ]