When a proper shunt circuit is connected with a curved piezoelectric membrane, its bended stiffness can be intensified. The system can be used for sound isolation. This mechatronic system， a typically multi-physics problem, was analyzed with FEM in detail. Frequency response characteristics were obtained when shunted with negative-capacitance in parallel. Transmission Loss was presented from 100Hz to 1000Hz. A wonderful sound isolation performance is obtained when shunted with proper values of negative capacitance. Negative capacitance and the loss of piezoelectric material are the main factors of the system. At some frequencies, the sound isolation performance can be increased when a compensated resistance paralleled with negative capacitance. This compensation is dependent on the frequencies. Due to its ordinary electrical parameters, the sound isolation system is realizable in practice. This sound isolation technology can be used in some fields such as windows of room and car.