Abstract: The longitudinal stiffness of an aerostat envelope is related with the pneumatic membrane structure that is analyzed in this paper. First, the scaling factor n and the internal overpressure p of the envelope configuration against the longitudinal concentrated load are obtained through theoretical analysis, together with the theoretical formula of the longitudinal stiffness. The theoretical analysis is validated by the FEM (finite element method) simulations and the test of a one-eighth scale model. The theoretical calculation method of the pneumatic membrane configuration stiffness in this paper could be used for the calculation of the mooring load of the aerostat.