Abstract: To study the high convergence of welding fatigue data distribution based on the mesh-insensitive structural stress, welding fatigue data coordinates were established based on nominal stress, structural stress and equivalent structural stress in principal S-N curve method from fatigue data of titanium alloy welded joints. S-N curves were fitted by least square method. The influences of welding factors on fatigue life were analyzed with rough set method by taking joints type, thickness, load ratio, ratio set as main influencing factors and taking the deviation of S-N data to S-N curve as decision attribute. Results indicated that the S-N data distribution based on mesh-insensitive structural stress are more concentrated and uniform. So it can be concluded that this method has a higher accuracy in predicting fatigue life of welding joint.