A new method to extract X-ray polycrystalline diffraction patterns diffracted from different depth in real scale is pnesented. In this method the X-ray polycrystalline diffraction data of surface layer are collected at different incident angles, and then the X-ray diffraction patters diffracted from thin sheets at different depth are extracted directly by some special mathematical method. So the depth profiles of peak intensity, peak position and line profile can be obtained quantitatively and nondestrnctively. The algorithm was deduced in theory, and the feasibility of this method was primarily tested with a Ni/Mo film sample with prefered orientation. This method has the prospective application in the area of the thin films and its reactions, interface and surface processing studies.