This paper presents a simplified mathematical model for the purpose of studying the resonant responses of a nonlinear dynamical system, (micro -electro -mechanical systems (MEMS)), which represented by a Van-der Pol equation subjected to a weakly non-linear parametric and forcing excitations. Using Multiple scales method, the Van-der Pol equation is transformed to a system of second order differential equation up to first order of small parameter ε. Three types of resonances are studied (harmonic resonance and subharmonic resonances of even order (onehalf and one -fourth )). The modulation equations for each resonances, steady state solutions, frequency-response equations, stability analysis are determined. Numerical analysis for frequency-response equations and stability conditions are carried out. Results are presented graphically by group of figures. Finally discussion for these figures are given.