Abstract: The detcrmination of uranium in HLLW by doublc isotope dilution mass spectrometry is described. Uranium is separated from HLLW by TBP/KeI-F reversed-phase partition chromatography. The spikes are enriched in ~(235)U and ~(238)U. respectively. The relative standard error is better than 0.1％ for the determination of uranium isotope abundance ratio by mass spectrometry. The blank value of whole procedure is 3×10 ~9g and the detectable limit of the method is 1×10~(-9)g for uranium. The uncertainty of the determination is 2％ for uranium content in HLLW.