Flutter widely happens on solar-powered aircrafts due to the slight stiffness and large deformation, so that it is significant to establish the dynamic model of solar-powered aircrafts and analyze the flutter characteristics. Based on an initial dynamic model of a 15 meters span solar-powered aircraft is firstly build, the reverse modeling is implemented by optimize the model stiffness according to the objective flutter speed. Then the flutter analysis is carried out and a complete method for flutter analysis of solar-powered aircrafts is developed. Utilizing this method for reverse modeling and flutter analysis of a long straight wing of a solar-powered aircraft, the wing spar stiffness is estimated according to the flutter speed object. In addition, it is shown that the flutter speed will increase by 29% as the wing torsional stiffness increases by 70%. The present method can be used for wing structure design of the 15 meters span solar-powered aircraft.