In the process of rotating bending fatigue experiment of aviation duct, due to the application of eccentric load, the mass distribution of deflection adjustment mechanism during rotation is uneven, which leads to circumferential wear and small clearance of the bearing connected to the offset control panel, and the actual measured peak-to-peak value is larger than the theoretical calculation value, which will affect the accuracy of the experiment. Therefore, the improvement scheme for mass balance was put forward.A balance lead block in the opposite direction of the movement of the offset plate was added to ensure that there would be no eccentric vibration, so the influence of excessive peak-to-peak value was eliminated. The results show that by using the proposed scheme, the influence of excessive peak value caused by uneven mass distribution can be eliminated.