Taking Hubei E-dong Yangtze River Highway Bridge as the engineering background, the finite element model of five exquisite segments of standard steel box girder is established by ANSYS to analyze the influence of six kinds of diaphragm spacing on the spatial distribution of torsional distortion normal stress of steel box girder subjected to eccentric load. The calculation analysis shows that the setting of transverse diaphragm can effectively restrain the warping and distortion effect of the box girder. The torsion distortion effect can be controlled in a small range when the standard steel box girder segment is set up with 3 transverse diaphragms.