The 5.5 m × 4 m aeroacoustic wind tunnel， as the first large aeroacoustic wind tunnel in China， was put into use at 2015， which filled the gap in the field of ground test research platform on aircraft aeroacoustic in China. In this work. The overall structure design of wind tunnel and detailed structure design of main sections are carried out in consideration of the wind tunnel characteristics including test capability on aeroacoustic， fast switching between open test status and closed test status and adaptability of model support system to test requirements under multiple working condition. The wind tunnel loop is made up of the replaceable large steel structure and concrete structure， which satisfies the multifunctional layout requirements of aerodynamics-acoustics and opening-closing status. The integrally movable multifunctional abdominal support device driven by handspike and the deeply embedded long stroke liftable tail support mechanism with the advantage of high accuracy are employed to achieve the fast switching between open test status and closed test status. The spherical wheel hub， the spherical blade with the adjustable blade angle and the locking structure between the flange and apical petiole are adopted to reduce the aerodynamic noise of blade root as far as possible and to achieve the reliable operation of fan rotor， which can satisfy the requirement of low noise of fan in combination of noise reduction measures taken at the wall. The test results show the safe and reliable operation of wind tunnel structure and the high test efficiency， which proves the success of structure design of 5.5 m × 4 m aeroacoustic wind tunnel.