Abstract: The conception of CAD （Computer Aided Design） is briefly discussed.Moreover, the application of expert system and fuzzy sets theory to CAD is described.Two examples of choosing structural type of airplane wings are given in this paper to illustrate the method discussed here.A degree of "satisfaction" for index of structural weight and cost is expressed by a value of the membership function of fuzzy sets.The membership functions embody experiences of experts.The results of the two examples are satisfactory.