Vortex-induced vibration characteristics of twin separate steel box girders in 4 different spacings under 7 different wind attacking angles ranging from -5° to +5° were investigated and compared with that of single steel box girder through sectional model wind tunnel tests. The 4 spacings are D/B=0.025（very small spacing），D/B=0.1（comparatively small spacing），D/B=0.4（medium spacing）and D/B=3.0（comparatively large spacing）, where D is net spacing between twin box girders and B is width of single box girder. The test results show that in very small spacing and medium spacing, vortex-induced vibrations of both windward box girder and leeward box girder are amplified. In comparatively small spacing，vortex-induced vibration characteristics of both windward box girder and leeward box girder are close to wind attacking angle. With decreasing of wind attacking angle, aerodynamic interference effect changes from suppression effect to amplification effect gradually. In comparatively large spacing，aerodynamic interference effect on vortex-induced vibration of windward box girder can be neglected. Vortex-induced vibration of leeward box girder is suppressed due to existence of windward box girder.