In this paper, the analysis of GexSi1-x/Si strained layer superlattice grown by MBE is made by means of X-ray double crystal diffraction. The structure parameters of GexSi1-x/Sisuperlattice is obtained from the simulation of rocking curve based on X-ray kinematical and dynamical diffraction theory respectively. The results calculated with these two theories is almost the same, there is a little difference only in the fine structure of rocking curve. For the high quality GexSi1-x/Si superlattice, the rocking cu rve calculated with X-ray dynamical theory is more close to the experimental curve than that with X-ray kinematical theory.