Abstract: In X-ray computed tomography,traditional reconstruction algorithm is based on the hypothesis that X-ray source is monochromatic.However,the actual X-ray source is polychromatic.So reconstructing image from polychromatic projections with traditional reconstruction algorithm can cause beam-hardening artifacts.This article separated the polychromatic energy spectrum into several sub-energy spectrum.And build the math model according to the regularity that the number of detected photons is in conformity to Poisson distribution.Then make parameter estimation with the statistical method on the basis of traditional reconstruction algorithm.Experimental result indicates that such method can remove the cupping artifact in reconstructed image effectively and improve the reconstructed image quality.