Since the aerodynamic stability is one of the most important issues to realize the long-span bridges, various studies were carried out and the latest findings were applied to the construction of the Honshu-Shikoku Bridges. However, the all countermeasure for aerodynamic stability may not be necessary at the maintenance stage. Therefore, it was required to confirm the aerodynamic stability of maintenance stage. In order to consider three dimensional effects, 3D flutter analysis which was developed for the Akashi-Kaikyo Bridge was carried out using the aerodynamic forces measured by the 2D wind tunnel test. As a result of this study, it was found that the aerodynamic stability is kept at maintenance work.