The reuse of machining process, by which the process for a new mechanical part is determined by referencing to the existing and matured processes, is an effective way of improving manufacturing and supporting innovation. To conduct the effective reuse it is necessary to express and retrieve a specific process. A kernel technique of the expression and the retrieval is to measure the similarity of part’s geometry variation during the machining. To address this problem, a general framework of measuring the similarity between parts is proposed in this work. The geometry variation sequence of intermediate process model is established, and then a method to measure its similarity is invented. Two case studies are rendered and the result reveals that the proposed method is effective and can provide the support for the process retrieval and reuse in industry.