In order to investigate the noise radiation of the symmetrical box girder structure and its influencing factors, the box girder of an elevated railway in Nanchang was examined. The structural noise in this box girder bridge was examined by using a hybrid finite element-statistical energy analysis model (FE-SEA) followed by simulation analysis and the findings were subsequently validated by using field tests. Accordingly, the influence of plate thickness on structural noise and the contribution of each box girder subsystem to the overall noise were analyzed. The results showed that the FE-SEA method is suitable for the studying structural noise in box girders. The peak noise frequency of the box girder structure ranges from 31.5 to 60 Hz. and the frequency of structural noise ranges from 50 to 160 Hz. The top plate and wing plate of the box girder contributed considerably to the far-field sound pressure level. The results indicated that increasing the thickness of each plate can reduce the structural noise, and this reduction is greater when the thickness of the top plate is increased. Therefore, in order to reduce vibration and noise in box girders, attention should be paid to the top and wing plates. In addition, we can increase the thickness of the top plate to reduce vibration and noise in box girders.