The laser beam with a flat top can increase the effectiveness of freckle removing by laser. In this paper the technical solution to remove freckle by laser is proposed with distortion lens to make Gaussian beam flat-topped off focus. The optical system and design requirement of distortion lens are given. Referring to the relevant literature, it is given that the flat-topped laser beam is gotten by the diffraction transform of the expanded and collimated Gaussian beam through the distortion lens, and computer simulations shows that the principle of freckle removing by laser and its technical approach is feasible. It can play an important role to improve the effect of freckle removing by laser.