Abstract: Fatigue crack propagation in welded joints is always accompanied by the phenomenon of crack closure. A new model of welded joints with mechanical heterogeneity was used for experimental and numerical analysis in this paper. Fatigue crack propagation and crack closure of welded joints was studied by experiment and finite element methods. Changes of stress distribution which ahead of crack tip was analyzed. It was found that, fatigue crack propagation in welded joints was affected by crack closure, the corresponding applied load when the stress σy at crack tip was zero can be taken as crack closed (opening) load P_op. The major role of mechanical heterogeneity in affecting fatigue crack propagation was also discussed.