During the flight, the wing structure will deform subjected to different external forces. Bending moment, as a kind of internal moment, has a close relationship with the force acting on the structure and the deformation size of the structure. Therefore, it is important to measure the bending moment for the aircraft condition monitoring under the deformation condition. In this paper, a bending moment measurement method based on fiber Bragg grating sensor was proposed by using the cantilever plate structure with an equivalentwidth, thickness and uniform cross section as a simplified model of wing structure. The strainbending moment transformation equation under the bending deformation condition was deduced. By building a bending moment monitoring system of unilateral clamped plate structure, the bending moment measurement of key positions on the plate structure under different loads was realized. The root mean square error values of the singlepoint load case, multipoints load case and uniform load case are 0.883, 0.825, 0.689 respectively.