The authors have collected airfoils used in training aircraft wings and provided a method of airfoil sellecting for wing design using rough set theory. Weight reflecting improtance of each factor is vital in evaluating or decision-making. The method of weight determining combined the attribute imporance with conditional information entropy, which was conformed in this paper by conducting a project of trainer wing design, is suitabale for airfoil selection in wing design. The number of breaking point in discretization of parameter of airfoil was studied. The authors advised that two breaking point method is preferable than one and three ones in limited number of airfoils in data base available. The method used in this paper is believed to be useful for trainer aircraft wing’s design.