Abstract: The spectral interferences derived from metal U,Pb,Hg and Tl,may occur when ICP-MS is used to determine ultratrace plutonium,but, which could be eliminated by the separation procedure using anion exchange resin.The plutonium in water is isolated with Fe(OH)_3 (coprecipitation),followed by purification using anion exchange resin with employing nitric acid and hydrochloric acid to rinse above mentioned ions. The eluate,0.01 mol/L HNO_3-0.01 mol/L HF,can be introduced directly to the sample injector,and is beneficial for the elimination of polyatomic PbCl~+. The concentration of ~(239)Pu in water is measured by isotope dilution using ~(242)Pu as the spike after the reported (ratio,)~(239)Pu/~(242)Pu,has been calibrated with the intensity of m/z 238 in the sample and m/z 239, m/z 242 in the aqueous solution of 2% nitric acid. The minimum detection limit (MDL) is 43 fg, and the lower limit of determination (LLD) is 88 fg. Among the samples analyzed,the amount of ~(239)Pu in the open area water is larger than the MDL,while it is lower than MDL in the deep well water,and the concentrations of ()~(239)Pu are 1.1 fg/L and 0.68 fg/L in the regional lake and river,respectively.