Abstract: In order to detect nuclear materials the study of the atomic number (Z) identification method based on scattering spectrum analysis and high Z characteristic of special nuclear materials was presened. The method can identify materials by detecting and analyzing positron annihilation photons, bremsstrahlung photons and Compton scattered photons produced by the interaction between X-ray and matter. The results of Monte Carlo simulation show that the method can discriminate Z effectively, especially for high Z materials. An experimental facility based on 7 MeV linac was set up for feasibility study and scattering spectra were observed with a LaBr₃(Ce) detector. Preliminary results verify that high Z materials can be discriminated successfully.