Abstract: Three-dimensional finite element method was employed toinvestigate the effect of the strength mismatching of the groove heamflange welds on the fracture toughness requirements in terms of crack tipopening displacement in welded beam-column connections,which provides valuable suggestions for the design of beam-column connections and selecting welding materials.The numerical results show that,for over-matching welded connections,column flange yields in a large scope,and fracture toughness demands are small.The plastic zone of the under matching weld zone is large,and there are large Von Mises stresses which facilitate the opening of the crack.Therefore,overmatching beam flangewelds can lower the possibility of brittle fracture of beam-column connections.Comparing the results obtained through experiments and finite element calculation,it can be concluded that the fracture resistance of beam-column connection using Q235B steel is rather poor.