A comprehensive model is a basis for adequately understanding the energy conversion mechanism of magnetostrictive materials and guides the design of magnetostrictive devices. This paper established a fully coupled model that fully considered the piezomagnetic effect and the electromagnetic effect in its procedure of energy conversion. The proposed model can accurately predict the output voltage with different excitation levels and illustrate the interaction between physical fields. Based on the established model, we quantify the voltage contributed by the piezomagnetic effect and the electromagnetic effect. After a thorough analysis, we discovered that even though the voltage generation is always dominated by the piezomagnetic effect of the magnetostrictive material, the proportion from the electromagnetic effect will increase moderately with larger excitation levels. In addition, the magnetostrictive effect toward the output performance is also discussed, which proved to lead to a marginal impact on the voltage waveform.