Abstract: The dual energy CT method can be used in nondestructive test for large size multilayer spherical shell with high density difference materials. Low Z materials basically have no barrier to high energy X-ray scanning, while low energy scanning will be truncated by high Z materials, hence image reconstruction methods need to be studied according to the dual energy X-ray projection features. The simulation model is designed according to the structure characteristics of the multilayer spherical shell, and projection sonograms for both high and low energy X-rays are simulated respectively, on this basis, images are reconstructed with Filtered Back Projection(FBP) or Algebraic Reconstruction Technique(ART) algorithm. Through a mass of simulation and comparative analysis, the conclusion is drawn that the F-R(fuse first and then reconstruct) method is better than the R-F(reconstruct first and then fuse) method for image reconstruction of the dual energy CT. It is pointed out that in order to ensure the image reconstruction quality, for the scanning X-ray energy choice, it is necessary not only to improve local projection quality, but also to minimize the total amount of the truncated projection.