Abstract: The fatigue assessment of welded joints of AZ31B magnesium alloy using point method(PM) and line method(LM) was studied.Both PM and LM belong to the critical distance method(CDM).Based on the local stress parameters of the two types of welded joints,butt joint and transverse cross-shaped joint,taken from fatigue test and finite element analysis,corresponding S-N curves were fitted.The comparing results show that the CDM approach can be used in fatigue assessment of the welded joints of AZ31B magnesium alloy,and its assessing results are consistent with the results of fatigue test.Further more,according to the magnitude of stress concentration,the CDM approach could prognosticate the location of fatigue fracture.The fatigue strength at 2×10⁶ cycles of both butt joints and transverse cross-shaped joints is calculated respectively,79.55 MPa and 49.10 MPa for the PM method,and 79.01 MPa and 44.38 MPa for LM method.