In the study of the cushioning characteristics of the airbag with constant venting area, based on the energy conservation principle and thermal dynamics equations, an analytical model of the airbag with constant venting area is proposed and validated by LS-DYNA and experiments. Then, the cushioning characteristics of the vertical cylindrical airbag with constant venting area are investigated with this model. A series of calculations are conducted to find out the influence of initial inflation pressure, vent area and the triggering condition of the venting orifice on cushioning properties. The initial limit pressure is defined. Numerical results show that the initial inflation pressure and triggering condition of the venting orifice are key parameters which affect the cushioning properties. When the initial inflation pressure is less than the initial limit pressure, the appropriate increase of initial inflation pressure and appropriate triggering condition reduce the volume of the airbag and maintain peak overload of the equipment at a reasonable level. The reasonable venting area can improve the energy absorbing ratio, reduce the peak overload and prevent the airbag rebound.