Abstract: This paper presents an improved constrained conjugate gradient reconstruction algorithm for flash radiographic image with low signal-to-noise ratio. A new preconditioned method is consummated which can more accurately reconstruct image’s axis of symmetry. The new convergence criterion and the substitution of relaxation step for optimal step in the one-dimension search are adopted to ensure the reconstruction accuracy and shorten the reconstruction time simultaneously. The numerical experiment results show that the improved algorithm has better general performance in iteration time and reconstruction quality compared with the original constrained conjugate gradient algorithm.