In order to solve the problem that the balance and model are easily damaged due to the excessive starting load when the supersonic wind tunnel is started or shut down, a method of suppressing the starting load with a flat device is designed. The structure and process of the test device are described in detail. Use aircraft model to carry out suppression effect test. And the changes of the starting load of the model with axial position, normal position and M are compared respectively. The results show that the device can reduce the starting load and vibration amplitude of the model at Mach 2.0-4.0, and has obvious suppression effect on lift, pitching moment and resistance.