Abstract: A numerical method is presented for predicting the aerodynamic characteristics of elastic aircraft under quasi-static approximation. This method can be used to evaluate the lift distribution and 11 main longitudinal aerodynamic derivatives of elastic aircraft at subsonic speeds. The aerodynamic calculations are based on the Green's function method. The structure deformation is evaluated by the free structure influence coefficient method. The combination of these methods can provide an efficient, general and flexible aerodynamic tool for design of elastic aircraft.Several numerical examples are given and some dynamical problems of elastic aircraft are also discussed in this paper. The derivatives evaluated in this paper can be directly adopted in analysis of stability and control of elastic aircraft.