Test generation is still a problem to design for testability and fault diagnosis for analog circuits. In this paper, an approach to sensitivity analysis based on signal flow graph (SFG) is presented and analyzed firstly. Then design technique for testability is studied in detail in terms of above approach. Furthermore, a prototype system for testing design by using Prolog and Matlab is presented. The approach and the design system are verified with a classical band-pass filter circuit and signal condition circuits of a Dynamic Tuned Gyroscope (DTG). The experimental results show they can be efficiently used to design for testability for a kind of analog circuits.