Abstract: On the basis of engineering elastic theory, structural analysis of flexible airship on stratospheric platform was conducted. Using nonmoment shell theory and virtual work principle respectively, the envelope stress and overall deflection were formulated for flexible airship. The deflection formula of inflatable fabric beam was extended to calculate the deflection of flexible airship with superposition principle, and the results of these two methods were validated. The critical loadcarrying moment and minimum pressure were presented for the airship in normal operation serviceability limit state. Eventually, buoyant center, gravity center, and other parameters of a 25meterslong demonstration airship were obtained, the minimum pressure of this airship was calculated, and the moment of flexible airship and corresponding deflection were investigated sequentially, providing valuable information for flexible airship designing.