In order to confirm that the effective notch stress method is applicable to the fatigue assessment of orthotropic steel bridge deck, the local stress characteristics of two different transition forms in the arc notch details of diaphragm was studied. The effective notch stress in the weld toe and the weld root of the rib-to-diaphragm was computed separately and compared. The result has shown that the crack is easier to generate in the weld toe. The experiment result was assessed by S-N curve, and the result has shown that the effective notch stress method is suitable for assessing orthotropic steel bridge deck. The notch radius was assumed to be zero and it would result in conservative results. Based on the comparison of different rib thickness, it is found that the crack initiation in the rib-to-diaphragm seems to be easier to generate with the increase of rib thickness. This study can provide important information for design of orthotropic steel bridge deck, as well as for the evaluation of the fatigue performance of orthotropic steel bridge deck.