Abstract: The method including the process of extraction chromatography and the mass spectrum measurement for the exact analysis of micro neptunium in the existence of large quantity of uranium is established. The key problems which influences the analysis of veracity are studied. The recovery of neptunium of the whole analysis procedure is more than 80% and the decontamination factor of uranium is more than 1×10 6 . This scheme is successfully used in the analysis of neptunium in aqueous uranium product of bench scale experiment.