Hard X-ray Modulation Telescope (HXMT) is China's first X-ray astronomical satellite. Low Energy X-ray Telescope (LE) is one of the HXMT's payloads, which used a special swept charge device (SCD) CCD236 detector to observed photons in an energy band of 0.7~13.0 keV. The CCD236 detectors need to be calibrated well before the launch of HXMT, including the calibration of the energy response matrix, which is the key to energy spectrum analysis. The output spectrum of CDD236 is not the actual emission spectrum of the observation source but the convolution result of the emission spectrum and the energy response matrix (RSP). Generally, we can apply a direct deconvolution method to restore the spectrum of the source. A general deconvolution algorithm is the Lucy-Richardson iterative method which uses the Bayes theorem of conditional probability to carry out repeated operations. Using this method, one can use the RSP to deconvolute with the output spectrum, and restoration of the actual spectrum can be obtained by this method. The spectrum of ⁵⁵Fe radioactive source can be restored using LR iterative algorithm for verifying the robustness of this method. After the iteration, the energy resolution is optimized from 144.3 to 65.6 eV @5.9 keV, and the continuous plateau is obviously suppressed. The restoration spectrum, which is composed of two Gaussian peaks with very narrow FWHM, can well characterize the structure of the real emission X-ray of ⁵⁵Fe. At the same time, the X-ray fluorescence spectrum of a composite was inversely solved by this method, and the X-ray fluorescence spectrum of the material was reproduced by iteration. The FWHM of each spectrum line was very small, and the main spectrum line of Ag element in the material was changed into an independent line spectrum by iteration. This kind of inverse energy spectrum can be well used for the analysis of element composition.