This paper deals with X-ray diffraction profile analysis for the sample with a micro-strain gradient in its surface layer. On the assumption that the variation of micro-strain L2> with depth t is expressed as L2>-Σam(L)tm, Warren-Averbach method is modified so that it can be used in this case. For the special case of L2>=α0+a1(L)t, the relationship between the micro-strain L2> and the depth t can be determined by analyses of diffraction profiles belonging to two different radiations.