To investigate the distribution patterns of the temperature field， residual stress field， and deformation field in welded joints of steel bridges， a 3D finite element model of a butt weld in a 16 mm-thick bridge steel plate was established using finite element software. The accuracy of the model was verified through the blind-hole method experimental data. Based on this validated model， the distribution characteristics of the temperature field， residual stress field， and deformation field in the welded components were further analyzed. Additionally， an initial crack was introduced into the weldment to explore the impact of initial defects and welding residual stress on the fatigue life of the weld. The study results indicate that along the direction perpendicular to the weld seam， the longitudinal residual stress exhibits a tensile-compressive distribution. Within the 60 mm heat-affected zone near the weld， tensile stress is predominant， with a peak value of 415 MPa， exceeding the yield strength of the material. As the distance from the heat-affected zone increases， the longitudinal tensile residual stress transitions to compressive stress. The transverse residual stress reaches its peak value of 205 MPa at the weld toe. Under unconstrained conditions， the welding-induced deformation presents as typical out-of-plane angular distortion， with deformation at each measurement point increasing linearly with distance from the weld seam center. The maximum deformation occurs at the outer edge of the weldment， measuring 14.58 mm. Even small residual stresses， regardless of their state， influence fatigue life. Residual tensile-compressive stresses of 3% and 8% result in a decrease of 16.7% and an increase of 68.4% in fatigue life， respectively. Residual tensile stress leads to a reduction in fatigue life as stress increases， but the rate of reduction gradually diminishes. When the tensile/compressive stress values are comparable， compressive stress has a far greater impact on fatigue life than tensile stress. During the prefabrication of actual components， methods such as pre-deformation should be employed to control the deformation of the weldment， while post-weld surface treatment techniques should be used to manage residual tensile stress， thereby improving material fatigue life and extending the service life of the structure.