Abstract: In the wind tunnel test of aircraft-taking-and-landing and vehicles, the fixed floor is used to simulate the ground. The existence of the fixed floor boundary layer has an influence on the test data. Generally in order to obtain full and reliable experimental data close to the ground state, various methods can be used to eliminate the boundary layer influence on the surface of the ground floor. Considering the effect and feasibility of large area fixed floor, we have put forward the suction control method of boundary layer thickness in the 8m×6m wind tunnel of China Aerodynamics Research and Development Center. The fixed floor with 48 suction units and 192 suction holes, which can be individually controlled, is developed. Based on the water ring vacuum pipe, a vacuum suction and control system is designed. Through the experiments, 10 kinds of boundary layer thickness control option are analyzed at the wind speed of 70m/s. Then we get the optimal control option with 30mm boundary layer thickness. At this optimal option, the influence on the flow angle is-0.14° and the height of the floor is also investigated. In the end, the suction floor system is applied in the wind tunnel test of C919, where it is found that at the angle of attack more than 8°, the lift coefficient decreases, the drag coefficient increases and the pitching moment increases.