Abstract: Numerical simulations of flow and aero-acoustics generated by the plate supporting high speed train model in aero-acoustic wind tunnel test are conducted to investigate the influence of the supporting plate on wind tunnel test and the causes. An optimization method of lengthening the plate is brought out based on the result of numerical simulations. Test results showed that the supporting plate caused deflection of the incoming flow, which changed air distribution taking place near the nose. This led to an impact on the unsteady flow, followed by a noise distribution change near nose and bogie. The lengthened plate reduced the deflection and made the flow and noise features much closer to the “without-plate” situation, indicating that this measure is useful for lowering the plate influence on high speed train aero-acoustic wind tunnel test.