A numerical method based on the techniques of inverse Fourier convolution and nonlinear least squear algorithm, etc. is presented for obtaining high-resolved spectra of radiation sources. This method can eliminate broadenings induced by radiation sources and spectrographs, and can improve the spetral resolution of spetrographs. As an example, the method is successfully applied to the analysis of laser plasma spectra of Mg ions recorded by pinhole crystal spetrograph.