In order to evaluate the fatigue stress level of the structural details of a steel box girder under the wheel load, the local fatigue stress of nine structural details were studied based on the stress influence line. The greatest stress amplitude was corrected according to the principle of damage equivalence, and the structural details of the steel box girder were divided. The results show that the vehicle load has little influence on the fatigue stress of the nine structural details of the steel box girder. At the intersection of the diaphragm plate, the roof, and the longitudinal rib, the influence on the stress occurred in the interval of the diaphragm plate. At the intersection of the diaphragm plate and the longitudinal rib, and at longitudinal rib joints and roof joints, the influence on the stress occurred at half of the interval of the diaphragm plate. The corrected equivalent stress amplitude was the greatest at the joint of the diaphragm plate and the longitudinal rib, and the smallest at longitudinal rib joints. With consideration of stress and construction quality, the fatigue stress of the structural details of the steel box girder can be classified into five levels, and the corresponding levels of the nine fatigue structural details are also provided.