The production of aircraft structure parts is featured by multiple varieties and small batches, which imposes significant challenges for the representation of process knowledge. Feature based method is an effective way as the process knowledge carrier. Although the parts are different from each other, they are composed of similar geometric features with similar machining processes. This paper introduces the concept of "dynamic machining feature" which is formed in the machining process and influenced by various real operations. In this paper, the process knowledge and interim geometric information are associated based on dynamic machining features. An ontology-based method has been adopted to represent relevant information of dynamic machining features. The proposed approach can speed up process decision and facilitate process optimization.