In recent years, parametrically MEMS resonators, characterized by their large response amplitude and low phase noise, have emerged as a focal point in the field of MEMS dynamics. This paper investigates the high-order nonlinear response of micro-mechanical beam resonators under strong parametric excitation, as well as the influence of electrothermal currents on parametric resonance response. Firstly, experimental data reveal that under strong parametric excitation, the amplitude-frequency response of micro-mechanical beam resonators no longer follows the Duffing hardening curve but exhibits a “tail-up” phenomenon in the latter half of the response curve. Subsequently to these observations, a parametric dynamic model of the nonlinear resonator is established. Theoretical analysis indicates that the “tail-up” phenomenon arises from the combined effects of nonlinear damping and high-order nonlinear stiffness. Furthermore, the paper investigates the influence of electrothermal currents on the parametric response of the beam. It is demonstrated that the introduction of electrothermal current increases the thermal elastic damping and axial stress of the micro-resonator, thereby significantly adjusting the response amplitude and resonance range.