Piezoelectric transformers are electronic devices made from piezoelectric materials. The piezoelectric transformers as the name implied are used for changing voltage signals from one level to another. Electrical energy carried with signals is transferred by means of mechanical vibration. Characterizing in both electrical and mechanical properties leads to extensively use and efficiency enhancement of piezoelectric transformers in various applications. In this paper, study and analysis of electrical and mechanical properties in forms of potential and displacement distribution throughout the volume, respectively, are discussed and especially focused on around its natural frequency. This paper proposes a set of quasi-static mathematical model of electro-mechanical coupling for piezoelectric transformer by using a set of partial differential equations. Computer-based simulation utilizing the three-dimensional finite element method (3-D FEM) is exploited as a tool for calculation in two purposes. The first use is developed the 3-D FEM for identifying its natural frequencies while the second use is for visualizing potentials and displacements distribution within the piezoelectric transformer. The computer simulation based on the use of the FEM has been developed in MATLAB programming environment. In addition, which satisfactory results of natural frequencies are compared with those obtained from the experiment and the accuracy of 3-D FEM model is confirmed.