Based on air wave theory and shell equilibrium analysis, a proximate analytic approach of mechanical impedance for bellows type air spring is presented by calculation of air pressure and shell stress field. The approach is the way that air spring is divided into several calculable regular simple regions according to superposition principle, then each region’s analytic solution is achieved combined with boundary and joint conditions and assembled to form parameterized expressions of air spring mechanical impedance. Finally an application instance of mechanical impedance calculation of marine air spring is given. And it shows that the method is feasible and provides a new idea of air spring dynamic characteristic analysis.