Software Testing, as an important phase in the life cycle of software development, is getting more and more recognition in recent years. While some work has been done in white-box verification, much less work has been done in black-box validation. This paper provides a novel approach named rough-hierarchical testing to test safety critical software as a black-box. The purpose is to find if the end product meets the requirement and has the expectant attributes. The method is elaborated at the beginning, then an illustration is introduced to demonstrate its feasibility.