The Cadmium Zinc Telluride (CdZnTe) semiconductor is recently utilized as a detector for the measurement of X-ray spectrum. In this paper, we calculate the energy absorption response of a CdZnTe semiconductor to mono-energetic photon beams by means of the Monte Carlo simulation, and investigate their energy dependence property. The photo-peak efficiency, which represents the detectable efficiency, and the fraction of K-escape showed three discontinuous points at same photon energies corresponding to the K-absorption edge of CdZnTe. X-ray spectra measured by a CdZnTe detector are different from the incident X-ray spectra, because of distortions caused by energy-absorption response of the detector. The net incident X-ray spectrum was well estimated by the stripping correction method using the response data of the detector to mono-energetic photon beams.