Abstract: Based on constrained conjugate gradient algorithm, a 3D constrained conjugate gradient algorithm (3D-CCG) is proposed for the reconstruction on high-energy radiography image. Constrained with prior knowledge, the reconstruction equation of 3D-CCG based on three-dimension reconstruction theory is solved by use of the preconditioned conjugate gradient algorithm. Numerical experiment results show that compared with the filter back projection algorithm and RPCCG, 3D-CCG is more efficient in reconstruction quality.