The attack-of-angle mechanism of FD12 wind tunnel is a hydraulic-driving mechanism with single side support.Its characteristics include clear interface between test section and diffuser, quick change of angle and strong adaptability.But when the attack-of-angle mechanism used during the operation of wind tunnel, the shortcoming of long stable time needed to position at any angle appears.Through the analysis on test conditions and mechanism movements, it is considered that it is the large moment of inertia of the model support and usage of single support for the mechanism that cause inconsistence between the movement direction of the piston rod in hydraulic cylinder and the direction of its output force, thus the hydraulic system become unstable, which is the reason of long time needed to position at any angle.To solve the problem, two kinds of methods were put forward.The first method is to improve the power of hydraulic system, using higher hydraulic pressure oil;the second method is using a mechanism to balance the moment of inertia of the model support.Through theoretical calculation and simulation test, the two methods were compared in their cost, difficulty in realization and reliability in operation, finally, the second method was adopted on the consideration of general request of the project.In the later tests, it is proved that the stable time of the attack-of-angle mechanism is shortened obviously.In this paper, the optimization process is introduced, the comparison of the two methods is described in details, meanwhile, the experimental results and photographs of the optimized attack-of-angle mechanism are given too.