Abstract: The authors present an algorithm which can estimate, by means of a standard cylinder or wedge model, the energy spectra of the CT system and the mass attenuation coefficient of the model at the same time. An algorithm on beam-hardening correction of CT image for single material object is presented as well. The simulation results show that the algorithm for estimation of the energy spectra can give a reasonable estimation of the energy spectra, and that beam-hardening correction algorithm is more precise than polynomial approximation correction algorithm and more rapid than common iterative algorithm.