Abstract In this work, nonlinear electromagnetic vibration energy harvesting from cantilever beam under base harmonic oscillation is investigated and the effects of electromagnetic parameters on behavior of system is considered. For modeling assumed mode method is used, and beam is modeled in according to Timoshenko theory, which includes shear deformation and rotary inertia. In energy harvesting, the frequency response of the system is very important because it shows the best areas for energy harvesting and it is a good criterion for designing energy harvesters, hence a semi analytical method is used to find simply the amplitude of oscillation in terms of excitation frequency. In this method, at first equations of motion are solved with complex averaging method and obtained equations are solved with continuation method. For validation, comparison between results obtained from numerical and semi analytical method is given. Also comparison between linear and nonlinear system, and stability of periodic response and their bifurcations are given. In addition, in order to the effect of number of mode shapes and convergence of solution, frequency response of one, two, three modes and four modes cases are compared with together.