Taking a suspension bridge with a streamlined girder of 1 660 m span as engineering background and using the methods of wind tunnel test and numerical simulation of CFD, this paper studies three main factors affecting the flutter stability of long-span suspension bridges, namely the main cable space form, aerodynamic shape of the girder section and height of central stabilizer, and then the mechanism of aerodynamic countermeasures is discussed. The results show that the influence of main cable layout on the flutter critical wind speed of bridge structures is mainly caused by the change of the torsional frequency of bridge structure according to the layout of main cables, which affects the critical wind speed of bridge structures. Appropriately increasing the ratio of width to height of the main girder section can effectively improve the flutter critical wind speed of bridge structures. Setting an appropriate height of central stabilizer can effectively improve the flutter critical wind speed of streamlined girder section with horizontal separation plates. The major effect of vortices generated near the central stabilizer is to generate the vertical aerodynamic force of streamlined main beam, leading to the increase of vertical movement degree of the main girder section and the suppression of torsional movement degree of the main girder section. Thus, the flutter stability of the streamlined girder section is improved.