As the software development cycles is getting shorter, the software reusability is emphasized accordingly. Specifically, the design reusability is being recognized as one of the most important factor to increase the software quality and productivity and make the maintenance cost down. Two essential abilities are needed to improve the design reusability. One is the identification of the reusable objects, and the other is the organization of the relationships among the objects. However, the existing methods using such as a grammatical analysis, a scenario matching and a unit of design problems(design pattern) have not been proposed proper principles to identify the reusable objects on the basis of the abstraction which is the core of the object-oriented concept. In this paper, we will offer the Two-Pass abstraction principle based in the abstraction concept.