Abstract: The conditions of non-structure surfaces in the enabled configuration views with two-side-multi-frame are studied. It is concluded that if the symmetrical similar-frame exists in the enabled configuration views with two-side-multi-frame, then the symmetrical similar-frame is the two non-structure surfaces in 3D shape. Corresponding similar-frame is a non-structure surface in 3D shape if there are not the common-plane point groups in this figure. Corresponding similar-frame is a forbidden surface in 3D shape when there are the common planes point group in the frames (non- triangle) and having a line of the frame intersecting or incline from the common planes point group. If one projection straight line corresponds to a closed-frame, and the line of frame does not coincide with part appearing on common planes point group in the frames, then the closed areas are a non-structure surface in 3D shape.

Key words: engineering graphics, 3D shape structure design, enabled configuration views, symmetrical similar-frame, corresponding similar-frame, non-structure surface