Abstract: We have developed the isotope dilution mass spectrometry with ~(233)U as a single internal standard. It can be used to determine accurately the abundant ratio in the uranium sample. It is an absolute measurement method based on gravimetry. The ~(233)U and the measured sample are mixed gravimetrically, then the R_(58)=~(235)U/~(238)U and R_(38)=~(233)U/~(238)U in the mixture are measured simuhaneosly, and the R_(38) can be considered as an internal reference standard. By means of the iteration operation, the R_(58) is close to its true value step by step. With this method, the total uncertainty of measured Rss can reach to 0.15％. This method has the obvious advantages, for example, its external precision is better than 0.02％.