For the requirement of wavefront correction of high power slab laser,two-dimensional beam expander shaping system is simulated by ZEMAX software.A rectangle beam of the initial size 2.5 mm×28 mm and divergence angle 7 mrad×2 mrad was expanded and shaped into a square beam with a size of 40 mm×40.2 mm and divergence angle of 0.54 mrad×1.3 mrad.Optical transfer function of the output light in beam shaping direction is close to the diffraction limit.When the beam shaping field is 10 mrad,the wave aberration is 0.0186 λ and P-V value changes less than 0.1 λ.