Abstract: To study the mechanism of aerodynamic interference of box girders with parallel double bluff bodies, the numerical calculation of double bluff box girders under winds of different spacing ratios was carried out. By comparing the calculation results with wind tunnel test data, it is shown that the variation law of the aerodynamic coefficients obtained by the numerical calculation is basically consistent with the wind tunnel test results. Therefore, the visual flow field distribution obtained by the numerical calculation can explain the aerodynamic interference mechanism. There are obvious whirlpools between the double bluff body box girders. This is the main reason why the drag coefficient of the upstream box girder decreases and that of the downstream box girder is negative. The wind suction effect of the roof of the downstream box girder is obviously weakened. This is the main reason why the lift of the downstream box girder decreases remarkably.