Abstract: Multi-channel soft X-ray spectrometers are used to detect the time history of radiation flux in ICF experiments. The responses of the spectrometer channels are linearly combined to get a equivalent flat response in order to calculate the radiation flux without unfolding. To deal with errors caused by the shapes of the spectra and local oscillations of the equivalent flat response, a method with weighting has been introduced. Flux recovery ratios of different methods for different spectrum shapes were compared. The improved method has been used to analyze ICF experiment data, and a modified time history of equivalent temperature was obtained.