T-welded joint was adopted as a research object and a structural multi-scale calculation program was proposed based on Arlequin algorithm on the general finite element program Abaqus platform in order to analyze the effects of welding details on ultra-low cycle fatigue performance of steel structures. Local elastic-plastic finite element analysis of T-welded joints were conducted, and the local plastic strain characteristics were analyzed. The effects of welding details, such as weld toe radius, unfused length of thick steel plate and unevenness of weld toe surface on local plastic strain history were compared. The ultra-low cycle fatigue characteristics of T-welded joints were discussed by qualitatively using Coffin-Manson model. The numerical calculation results show that weld toe position is the vulnerable position of T-welded joints, and the influence of the unfused length of the steel plates on the local plastic strain history of the welded part is negligible. The local plastic strain history is more sensitive to the change of the weld toe radius, and the increase of the weld toe radius can significantly improve the ultra-low cycle fatigue performance of the structure under cyclic loading. The flatness of weld surfaces is an important factor on the plastic strain history of welding areas. Sharp dents can significantly reduce the ultra-low cycle fatigue performance of welded joints whereas a smoother welding surface is beneficial to reduce the local plastic strain and improve the ultra-low cycle fatigue strength of joints.