It is hard to design for beam expander with high power and wide aperture required, because it is shorten length, larger aperture, as well as on axis and off axis aberration must be corrected properly. In this paper,a design method for high power and wide aperture beam expander is talked about. One beam expander is given with clear aperture of 200mm, focal length of 400 mm and field of view of 2 mrad. Image evaluation and system parameter are shown at same time.