The approaches to reduce wind-induced vibration of long-span bridges can be classified into aerodynamic one and machine one. Among them, the study of former approach has great influence on engineering and economy.In order to improve aerodynamic stability of bridge deck, this paper has studied the flutter characteristic of separated deck on the basis of some cross-sea bridge in china with separated box girder by use of section model wind tunnel test. Firstly, this thesis introduced the process of calculating the dynamic characteristic of the project bridge, and then described the two-dimension and three-dimension coupled-flutter theory of long-span bridges with studying the flutter characteristic of the suspension bridge.In order to analysis the aerodynamic characteristic of this separated section, this thesis computed the static three component force coefficient, the results showed the separated girder had better aerostatics stability.As to wind tunnel test, the flutter onset wind speed of separated section and single box-girder were firstly and directly measured by the test .The test results indicated that slotting at the cross section center was a valuable approach to enhance the flutter stability of long-span suspension bridge. The modified form coefficient of that separated section was also measured with the changing of the natural frequency ratio by wind tunnel test. It was found that the slotting results were less influenced by the changing of the natural frequency ratio.