Structural modal coupling is one of the problems which must be solved in FBW (Fly-By-Wire) control law design. Firstly, the advanced technologies of foreign civil aircrafts are analyzed. Then, the design methods of structural notch filter and structural modal suppression and the issues that should be taken into consideration in the design are researched. The feasibility of the method is verified by using an example aircraft. Finally, the principles and methods of ground tests are described briefly.