Abstract: Reversed modeling is the critical technique in analyzing and understanding object-oriented software, which is also the basis of its testing and maintenance.A set of basic rules for reversedly constructing program's class models are studied, and an inheritance-layered class diagram is proposed, which can be drawn automatically. Kinds of relationship, such as inheritance, composition and association, can be shown in the layered class diagram. By the diagram, relativity and dependency among classes can be simply highlighted. In the end, the revised modeling tool, SafePro/Re-OM, based on the set of rules, is presented.