Abstract Stationary and dynamic wind tunnel tests of twin box girders with a space ratio of L/D=1.70 have been performed in this study. The vortex-shedding phenomenon under stationary and dynamic conditions and vortex-induced vibration are observed and analyzed. The results indicate that regular vortex shedding occurs only at the trailing edge of the downstream box girder under stationary conditions. Although the strength of the vortex is very weak under stationary conditions, it gives rise to vortex-induced vibrations with a lock-in range of 0.570≤Ur≤0.668 in dynamic testing. The higher harmonics of wind speed around the body is observed and is attributed to nonlinear effects from aerodynamic forces. To further study the flow characteristics around the twin box girder when undergoing vortex-induced vibration, a hybrid method combining experiments with numerical simulations is employed. The pressure distributions, energy transfer between the flow and motion of the body, and evolution of flow patterns over vortex-induced vibration process are analyzed based on the computational results. The results indicate that with an increase in oscillation amplitude, strong vortices form in the gap between the two box girders. These vortices impinge on the windward wall of the downstream box girder and cause the flow to separate and re-attach periodically around the windward corners of the downstream box girder. Based on the analysis of the vortices in the gap, five control measures are used in the wind tunnel test to suppress the vortex-induced vibration of the twin box girders, and the most effective control scheme is obtained.