The piezoelectric energy harvesting device relies on the energy extraction circuit, the energy extraction efficiency of traditional standard circuit is not high, and the synchronous switch circuit can effectively improve the energy extraction efficiency. In this paper, the use of viscous material as the moving electrode of adaptive mechanical switch structure is proposed. It does not require additional electronic devices and can adapt to the displacement amplitude of the cantilever beam to harvest higher power. The sinusoidal excitation and noise excitation are used to analyze the parameters of the viscous material. The results show that when the excitation is different, the parameter selection of the viscous material is also different, which also proves the performance of the adaptive mechanical switch.