Abstract: Based on the damage model under a monotonic loading condition, a new damage model is developed to predict the ultra low cycle fatigue failure of building structural steel subjected to seismic actions. The damage prediction model was implemented in commercial finite element software ABAQUS by using the user material subroutine. Then, parameters used in the damage model of building structural steel base metal, heat affected zone and weld metal were calibrated respectively through monotonic loading tests and ultra low cyclic loading tests of notched coupon specimens, in addition, the damage evolution laws at the center of notched specimen under different loading conditions were compared. It can be observed from the comparison that crack always initiates in the center of specimens, which is consisted with the test results. Finally, the damage model were applied to investigate the damage evolution of beam to column welded joints under ultra low cyclic loading history. The fracture process was simulated and the number of cycles to fracture was predicted, which agrees well with the experimental results.