The damping property of a pneumatic suspension with orifice-type fluidic resistance is characterized in this study. The nonlinear and linear models for the suspension system are first formulated and experimentally verified. The verified linear model is employed to derive a new pneumatic damping measure, equivalent damping ratio, based on which a pneumatic Damping Ratio Diagram (PDRD) is proposed. A systematic investigation on pneumatic suspension damping is then conducted. The results and analyses demonstrate that PDRD can be an effective tool for the calculation/design of pneumatic damping, where to properly choose pneumatic suspension design parameters can help yield desirable pneumatic damping.