Wind tunnel tests of the sectional models of twin parallel box girders with bluff body in medial distance are performed. Aerodynamic interference effect of twin box girders is studied and influence of aerodynamic interference effect on aerodynamic coefficients and vortex-induced vibration are analyzed. For test of aerodynamic coefficients, the wind attacking angle is ranging from -10°to 10° and D/B (ratio of net spacing of twin box girder models and width of single box girder model)is ranging from 0.4 to 1. For test of vortex-induced vibration, the wind attacking angle is ranging from -4°to 4 and D/B is 0.8. The research results show that aerodynamic interference effect on aerodynamic coefficients of forward box girder can be neglected. Aerodynamic interference effect on aerodynamic coefficients of leeward box girder is shown as reducing effect. Under zero and negative wind attacking angles，aerodynamic interference effect on vortex-induced vibration is slight for forward box girder and shown as remarkable amplification effect for leeward box girder. Under positive wind attacking angles，aerodynamic interference effect on vortex-induced vibration is slight for leeward box girder and shown as remarkable reducing effect for forward box girder.