Breathing sound reflects the respiratory status, such as a state of airway, effort of respiration, alteration of sound induced by disease, and so on. We have been developing a breath sound sensor with improved acoustic impedance matching. In this paper, we compared two simulation methods based on the frequency characteristics of sensor. First of all, we executed numerical analysis of breath sound sensor, based on the electrical equivalent circuit model. Next, we used the FEM to simulate compared with the numerical simulation in electrical equivalent circuit model. The reason why to use FEM was that FEM could simulate the various conditions of sensor parameter. From the results, we concluded FEM simulation was more useful.