To solve the problem of limited experimental resources and high equipment maintenance requirements in the course of "weak signal detection", a combination of Proteus simulation and experimental teaching mode is proposed. Learning examples of lock-in amplifier which is the most important technology of the weak signal detection, the students can develop a virtual lock-in amplifier with the software of Proteus. In this process, the students not only get familiar with the structure and principle of the lock-in amplifier, but also master the Proteus simulation techniques. The new teaching mode helps students build the process by themselves and prepare them for the next experiment.