In this paper, taking the large aspect ratio wing as a research object, and combined with the geometric nonlinear structure finite element modeling method and the nonlinear aerodynamic calculation technology, a interpolation method is proposed to solve the geometically nonlinear aeroelastic problem. Taking a scaled model of solar UAV wing as an example, the calculation and analysis and experimental research are carried out. The resuts show that the nonlinear flutter solution obtained by the method in this paper is basically the same as that obtained by the conventional method. By so doing, not only the calculation efficiency is doubled, but also the serious calculation deviation may be avoided in the conventional method, which may result from the unreasonable setting of the calculation working condition.