Abstract: ray spectrometry is a passive non destructive assay technology. It's very simple, fast and accurate in determining the isotopic abundance of uranium and plutonium. Accurate determination of isotopic abundance of U or Pu is very important for material control and accountability. The principle of γ ray isotopic analysis in determining abundance of U and Pu is emphasized.The methods and results of the measurement are also presented. The results indicate that the isotopic abundance in the sample can be determined within 2% error using a HPGe system.