The stress change of membrane flapping-wing aerial vehicle that used Moon-Rivlin model was calculated in one flapping cycle. One flapping cycle was divided into twelve segments, aerodynamic force and inertia force in each segment were calculated, the stress distribution could be gotten. The results show that: at the beginning of upstroke and at the beginning of downstroke, the stress of flapping-wing is maximum; the stress of downstroke near the flapping symmetry position is minimum, and the stress of upstroke near flapping symmetry position is another minimum peak stage.