Three-Dimensional machining process planning is the important part of the manufacturing industry informationization, of which manufacturing feature recognition is the core technology which is the prerequisites of machining process planning. Its data mainly comes from the basal B-Rep(Boundary Representation) information of three-dimensional model. This paper focuses on the pivotal technic and difficulty of B-Rep information's extraction in CATIA which is commonly used in auto trade, describing how to apply CAA secondary development technology in depth, extract B-Rep information and use it to feature recognition technic of three-dimensional machining process planning system, providing a basis for machining process planning.