A flight loads analysis framework was devised to consider the geometrical nonlinear effect and the surface aerodynamic effect for flexible aircraft. The structure consisted of joined nonlinear Euler beams allowing arbitrarily large deformations, while the lifting surface model employed span-wise and chord-wise vortex ring lattice. The core algorithms were to dynamically modify the aerodynamic influence coefficient matrix by the surface lattice associated with deformations, and to iterate the computation until the deformations converged. The proposed method was applied to two models. The results for small deformations agree with the linear method, whereas for large deformations, a significant variation has arisen due to the surface aerodynamics. This approach proved to be more accurate than the conventional linear method under large deformations, and feasible for engineering analysis.