Abstract: Gust response analysis plays an important role in large commercial plane structural design. Gust alleviation by active deflecting control surfaces is a pivotal technique for future aircraft design. Based on CFD/CSD time simulation method, considering gust as the input of the system and the root bending moment as the output, we build a gust response analysis model in state-space by using system identification in transonic flow. Similarly, considering aileron deflexion as the input and the root bending moment as the output, we build an aileron deflexion response analysis model. By coupling the two models, a gust alleviation analysis model is constructed in state-space. Then the optimal control method based on state feedback is used to design the active control law, and an observation device is designed to attain the state variable. Finally, the effectiveness of the designed control law is validated through a numerical simulation. The wing root bending moment can be decreased up to 60%-80%.