X-ray double crystal topography method with non-parallel asymmetrical (+
-) setting and the study on GaAs/AlGaAs epitaxial crystal are given in this paper. The diffracted effects of bending crystal plane resulted from epitaxy are analysed.From the topographies of substrate and epitaxial layers on MBE
misfit dislocations
line dislocations
growth hillock
defects from pollution and misorientation are discussed.The origination and developement of defects and dislocations are explained from the processes and principle. It is found that the MBE growth GaAs/AlGaAs epitaxy can be improved by the insert of a serial strain super lattices.