In product design, the matter of form is very important. Considering that product design is a work of creating the form having a synthetic function, while grasping the structual visual order of the form, it can be regarded as a process of seeking a change in the forms ultimately. Therefore, in design, the matter of the form is not a kind that can be simply solved by the thinking of the designer. It can be proved more clearly through systematic experiment and research. Dealing with the form is by no means easy. This is because the product form should take into account synthetic form factors by considering various and manifold related important elements. These include the problems of style, production process, distribution process, problems arising from the relationship with customers, and influence on the environment. If various geometric forms such as a hexahedron, cylinder or cone are not related organically and compositely with each other, the optimal design cannot be obtained. A study of the form, in order to solve such problems, is performed in many fields from various angles. The well-defined form is based on the exact same principles as are used in the stable iron frames of well-constructed buildings. Such modeling principles shoud be closely considered in order to identify the form exactly in the product design and produce the forms creatively. The study considered instances where the mutual intersectional form principles were applied in three-dimensional basic modeling for the product designs. A concept of the intersectional form can best be understood only in TV, Audio, Washine machine and Computer that give simple images. Since space and form are dismantled logically in the order of movement volume, surface, line and point from the internal structure, this principle is an important factor in grasping the product forms producing the geometric solid figuratively. However, with only one mutual intersectional principle of the form, it is impossible to explain the whole shaping factor of the forms. Therefore, III three-dimensional basic modeling, the study suggests the necessary conditions, in order to solve the matter of the form of design only under the mutual intersectional form, as one of the important principles in producing the design forms.