In order to make analysis for testability of hierarchy system, a testability modeling and analyzing approach were proposed for hierarchy system based on multi-signal flow graph (MSFG). This approach can used MSFG to build hierarchy system's hierarchy structural mode. Firstly, dependency model was applied to make testability analysis for the top-model. If the hierarchy module can't be isolated ... [Show full abstract] with other modules, the dependency model was used to make testability analysis for the ambiguity again, continuing this process until realizing diagnostic designing of the whole hierarchy system. Finally, by applying the proposed approach in some hierarchy structural amplifier/filter system, the efficiency of this method was verified, and the result shows that this method is efficient, and effective diagnostic strategy can be obtained for the testability analysis of hierarchy system.