A new method of quantitative X-ray diffraction (XRD) analysis that can be named as computed depth profiling of X-ray polycrystalline diffraction patterns has been developed. In this method, the XRD data are collected at different incident angles, and then the XRD pattern diffracted from a thin layer at certain depth is solved by a mathematical method. The algorithm was deduced theoretically, and the feasibility lest of this method was performed with a Ni/Mo film sample. This method has the prospective application not only in non-destructive testing of the depth profile of the peak intensity, peak position and line profile quantitatively, but also in the analysis of thin surface and interface layers.