In this paper, the characteristic of the stiffness and damping of the air spring is presented at first. Then the dynamical and mathematical model of the membranetyped air spring in car suspension is established, where only the vertical motion of the body is considered. Moreover, the main resonance of a singledegree- of-freedom system with the membrane-typed air spring is researched by multi-scale method. The stationary solution of this system is analyzed, and the theoretical amplitude frequency response is also obtained. It is calculated by Substituting the actual value of parameters, the curve of excitation amplitude and excitation frequency are gained. The affect of excitation amplitude, excitation frequency and the nonlinear stiffness is analyzed. Based on the singularity theory, it could be found that the response is the universal unfolding of the pitchfork bifurcation, which indicated the relationship between the response and the excitation amplitude, and the non-linear stiffness.