The energy harvesting of a piezoelectric cantilever beam is obtained from the excitation of vibration modes. Vibration modes have strain nodes where the strain distribution changes in the direction of the beam length. Covering the strain nodes of the vibration modes with continuous electrodes effects a cancellation of the voltages outputs. The use of segmented electrodes avoids cancellations of the voltage for multi-mode vibration. The theory of Gauss law is presented for the voltage response due to the electro mechanic coupling. The effective parameter in the voltage response is the modal coupling term. This parameter depends on geometry, material, piezoelectric coefficients and the Eigen function of bending slope. If the slopes of the electrodes boundaries are close together, the electric response of vibration mode is very small. The resistive load affects the voltage and generated power. The optimum resistive load is considered for segmented and continuous electrodes, and then the power output is verified. One of the effective parameters on energy harvesting performance is the existence of concentrated mass. This topic is studied in this paper. Resonance and off-resonance cases are considered for the harvester. In this paper, both theoretical and experimental methods are used for satisfactory results.