In order to investigate the problem whether resolving power for aberration image of light beam can be improved by increasing the amplification ratio of optical device, the shape distortion of small light beam passing through compressible mixing layer has been researched. The experimental aberration image of small light beam has been obtained using CCD camera imaging system, then a two-dimensional biorthogonal wavelet transform and Canny edge test technique have also been adopted to treat with the aberration image. Using these techniques, the edge of zero-order diffraction spot has been identified clearly. In addition, comparing perimeter of beam with its area, it is more suitable for using area to describe image distortion than for its perimeter.