Due to the lack of discussion on the design methods of latch, monostable circuit and multivibrator in textbooks, the internal relationship of these three kind circuits was studied from the demand of circuit storage signal. It was found that the monostable circuit and multivibrator can be realized by charging and discharging the capacitor which was connected to the latch, then the design methods of latch, monostable circuit and multivibrator were derived, and they were taught in the university courses. The new approach is conducive to students' learning on the design of these three circuits, help them to understand the performing principle of these three circuits, and train students' ability to investigate the essence and internal relationship of circuits.