This paper presents to verify the energy harvesting of a nonlinear piezoelectric multilayer beam under harmonic excitation. For getting the perfect performance in energy harvesting, the effect of the energy loss factor, resistive load, and excitation frequency are studied on the results of the power and voltage generated. In this paper, a numerical program is developed with matlab software. Numerical approximation of the nonlinear equations uses a mixed finite element formulation in terms of displacement and potential electrical variables. To verify the numerical results, the experimental results for the energy harvesting of a piezoelectric multilayer beam with harmonic base excitation are used. The multilayer piezoelectric beam (MPB) used consists of two bimorphs in the case of a series connection and a substructure layer of aluminum. For the considered electrical circuit, the piezoelectric energy harvesting model is connected to the resistive load and the generated power in MPB is sent to load resistance. The influence of the type of layer connection on the output voltage value is investigated. The generated voltage and electrical power of the resistive load are verified using the piezoelectric multilayer beam in both resonance and off-resonance cases. According to the results, the maximum value of electric power occurs at the optimum resistive load for the selected frequency value and the behavior of energy harvesting depends greatly on the excitation frequency. Also, the value of the capacitance and resistive load affects the voltage and power generated, and optimum resistance is vital for producing maximum power.