In the present study, a kind of broadening algorithm method for simulated spectrum was developed by using the detector response function (DRF), which can be used to reduce the differences between Monte Carlo simulated element characteristic X-ray spectrum and experimental spectrum. First of all, based on in-depth study on previous works of others, we established a kind of detector response function model with strong generality for Si-PIN semiconductor detector. Weighted nonlinear least-square method is used to fit the X-ray spectrum of standard single element, and parameters can be obtained simultaneously. Then these parameters are normalized to get the normalized response function R(E, E′), which will be used to broaden the simulated flux spectrum. Secondly, R(E, E′) is used to broaden and transform the simulated flux spectrum. Then pulse height spectrum (PHS) is obtained to match experiment spectrum. This procedure can obtain the X-ray spectrum conveniently only by using MCNP simulation; moreover, simulated spectrum and experimental spectrum have high consistency. Finally, the simulated spectrum was achieved to match the experimental spectrum. Ten elements (Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As and Sn) K doublet X-ray full energy peak was fitted by the proposed DRF model, and reduced chi-square values for each were in the range of 1.04～1.18. The simulated flux spectrum of a copper alloy sample containing six kinds of elements was transformed and matched the experimental spectrum really well, and the complex overlapped spectrum was resolved.