Abstract: In order to recognize the open-closed angle feature(OCAF) in aircraft structural parts, an approach based on the main face extension is presented. The method relies on the generalized pocket model. First, the faces of OCAF in the generalized pocket are recognized and the set of main faces are obtained. Then, the set of main faces and the set of related faces are extended to get the intact geometric attributes of OCAF. Meanwhile, the types of faces in the set of main faces are decided. Finally, according to the geometric attributes, the OCAF feature in generalized pocket is recognized and its relevance tree of a part is constructed. The validity and accuracy of this approach are verified through examples.