Abstract: An approach to evaluate the strength of welded joints with mechanical heterogeneity was proposed.The hardness measurement and tensile testing were performed on the specimens,which were cut from the undermatching joints of pipeline steel.According to the relation between hardness and strength for metals,methods were developed to determine the yield stress,true stress at maximum load and work hardening component from the hardness measurement.Thereby the local material properties across welded joints could be obtained from the hardness distribution on them.Finite element model of welded joints was constructed to calculate their yield strengths and tensile strengths.In this model weld and heat affected zone were divided into small partitions to be given the special material properties.Comparison between the results from finite element analysis and tensile test showed that,with this model,the strength of welded joints with mechanical heterogeneity could be predicted with an accuracy of ±40 MPa.