In the last few years, piezoelectric materials have been widely used for vibration energy harvesting due to its efficiency for converting mechanical energy into electrical one. In the literature, various approaches have been devoted for modeling the piezoelectric harvesters in order to predict its electromechanical coupling responses. In this paper, we present a finite element modeling of a bimorph piezoelectric harvester as typical cantilever beam which is composed of an elastic substrate covered by two piezoceramic layers. The generated electricity is due to the vibration of the host structure. The main purpose of this work is to develop a reduced order model able to predict the responses of the harvester and to improve simulation efficiency with a low computation cost. In order to reach this goal, the electromechanical problem is projected on a truncated eigenvectors basis with short-circuited boundary conditions. Furthermore, a numerical example of a bimorph harvester as case study is presented and analyzed. Through this example, the effect of the basis truncation on the electromechanical outputs is discussed in term of computation error and time. Results show that for an optimal truncated basis, the reduced order model gives good results in comparison to the direct methods with lower cost of calculation.