Aiming at the S355 J2 W+N butt joint with a thickness of 12 mm plate,the influence law of geometrical parameters such as residual height H of weld seam and weld fusion width W of weld seam on stress concentration at weld toe was investigated by using finite element calculation method,and the empirical equation of stress concentration coefficient at weld toe was obtained by regression analysis. The results show that:both weld width and weld residual height have effects on the stress concentration factor H,but the variation of residual height has great effects on the stress concentration at the weld toe. Under the same weld width,the stress concentration coefficient Ktof weld toe increases with the increase of residual height,and the maximum increase is 33.19%. When 1.0 mm