A coupled stress analysis model that considers the welding residual stress and vehicle stress was established in order to accurately analyze the influence of the actual tension and compression state and stress ratio at the deck-to-rib welding seam position on the fatigue life of an orthotropic steel deck (OSD). The calculation of the fatigue parameters, including the stress ratio and equivalent stress amplitude, enables the development of a refined calculation method for the coupling stress between the welding residual stress and vehicle stress. A qualitative analysis of the fatigue life under the vehicle load and residual stress field was conducted using the proposed method by taking the Jiangyin Yangtze River Bridge as an example. A case analysis show that when the residual tensile stress in the welding seam position is superimposed on the mainly tensile cyclic vehicle load stress, the longitudinal and transverse stress relaxation exceeds the peak vehicle load stress and significant stress relaxation occurred. When the residual tensile stress in the welding seam position is superimposed on the mainly compressive cyclic vehicle load stress, the relaxations of both the longitudinal and transverse stresses are not obvious. Compared with the stress state of the welding point under the action of only the vehicle stress, when the coupling effect of the welding residual stress and vehicle stress is considered, the fatigue stress state of the welding point has undergone an essential change under cyclic compressive stress, that is, the compressive stress state that does not require a fatigue check is changed to the tensile stress state. Although the fatigue state of the tensile stress cycle condition has not changed, the fatigue life of the welding point changes from infinite to finite under the tensile condition.