Abstract: A special assay method that determining the high energy gamma ray 2 614.75 keV from 208Tl, the daughter of 232U is presented. By which the attributes of uranium can be learned about. The theoretical analysis and experiment results prove that HEU from U-Pu cycle contains a few 232U. The gamma ray 2 614.75 keV can be detected even under the condition of thick shield. It is proved that this method is feasible to determine HEU.