Abstract: To enhance the static and fatigue strength of undermatching butt joint of high strength steel under transverse loading, the influences of geometric parameters such as excess of weld metal, radius of curvature at weld toe, plate thickness and total width of cover pass in butt-welded joint on stress concentration factors at weld toe and weld root were studied by finite element method.Based on these simulation results, the empirical equations of stress concentration factors at weld toe and weld root were obtained by regression analysis, which offers a significant guide for joint design of undermatching butt joint of high strength steel.