A new method based on SMA is studied to control the stiffness of structure in the context of aerodynamic heating of supersonic aircraft. The variable-stiffness rudder structure of strengthening rib replaced by SMA strips is proposed. The results show that the stiffness of the structure can be passively controlled by making use of the feature that the elastic modulus of austenitic phase is higher than that of martensitic phase under a high temperature. Besides, the first order natural frequency of the structure can increase by 10% after the control system works. Furthermore, the changing of stiffness of the structure with the environmental temperature increasing is also studied. An active control system is established because the phase transition of SMA could not be fully completed under the environmental temperature.The experimental results indicate that the instantaneous discharge of large capacitors is used to drive SMA in order to complete the phase transition. The response time of SMA can reach 15ms. In addition, as the temperature increases, the stiffness of structure decreases initially, and then increases gradually. When the temperature is equal to the austenitic finish temperature at zero stress, the stiffness achieves maximum value. After that, it decreases slowly.