Abstract: The fatigue notch factors of welded joints are expressed in terms of hot spot stress serving as controlling stress,and obtained on the basis of Taylor's Critical Distance Theory,corresponding to three approaches to determine hot spot stress.The effects of joint types,weld sizes,main plate thickness and the methods to determine the hot spot stresses on the fatigue assessment of welded joints are examined with the analysis of fatigue notch factors.The results show that the influence of weld size and the web plate thickness on the scatter of fatigue notch factors is small in contrary to the obvious effect of the main plate thickness,and the latter is predicted for welded joints of fillet welds and butt welds respectively by means of fatigue notch factors and is found to be in good agreement with existing empirical relation.Also it is indicated that the two types of extrapolation method to obtain hot spot stresses are valid in reducing the diversity of fatigue data and the dependence of fatigue data on the types of joints and loading conditions.