介绍直接工程的概念。给出直接工程环境下变异设计的抽象描述 ,并分析其特点。对变异设计中的相似性类型进行研究 ,提出基于总体层和特征层相似性比较的变异工艺设计方法 ,给出有关相似元的比较算法。该方法已用于指导实用型 CAPP系统的开发 Introduce the concept of direct engineering. The abstract description of mutation design in direct engineering environment is given and its characteristics are analyzed. The similarity types in the variation design are studied, and the variation process design method based on the comparison of the similarity of the whole layer and the characteristic layer is proposed, and the comparison algorithm of similar elements is given. This method has been used to guide the development of a practical CAPP system