This paper was concerned with the validity and applicability of local approaches used for the fatigue assessment of welded joints. The equivalent stress was introduced according to Taylor's critic distance theory classified as local approaches，and determined in the finite element method. The fatigue data of both steel and aluminium cruciform joints were analyzed. The fatigue failure might originate from weld toes and roots in load-carrying cruciform joints. The analysis results have shown that the equivalent stress can be used to predict the position where fatigue failures occur. The data of fatigue strength and stress-life were examined in terms of equivalent stress. It has been shown that the data scattering is remarkably reduced for cruciform joints with fatigue failure originating from weld toes. Then, the unified strength and S-N curve can be expected to be determined, but it is not the same for cruciform joints with fatigue failure originating from weld roots. The data scattering is high and comparable with the case where fatigue strength is expressed in terms of nominal stress. The latter indicates that the validity of local approaches is absent and its applicability needs further studies.