The initial welding defect is the key factor that affects the fatigue performance of the structural details of the orthotropic steel bridge deck. In order to study the whole life cycle dynamic characteristics of crack initiation and propagation of the joint weld between the top plate and the longitudinal rib of the orthotropic steel bridge deck, based on the fracture mechanics theory and ABAQUS-FRANC3D interactive technology, the dynamic characteristics of the stress intensity factor in the whole process from the weld buried defect to the fatigue fracture were studied, the crack shape development law was revealed, and the influence of sensitive parameters on the crack growth rate and fatigue life was analyzed, the full-life propagation behaviour of fatigue crack is clarified, and the reliability of the research results is verified by the full-scale segmental fatigue test of steel bridge deck. The analysis results show that the fatigue crack growth behavior of steel bridge deck can be divided into three stages: burial stage, initiation stage, and propagation stage. The distribution of stress intensity factors in the buried initiation stage and the propagation stage along different crack paths are exactly opposite; buried cracks of any initial shape tend to be round with continuous expansion, and surface cracks of any shape gradually flatten, which reasonably explains the flat shape of surface cracks when they continue to extend to the roof; the crack propagation rate along the upper surface of the buried stage is 54% higher than that along the lower surface. The crack propagation rate from the buried initiation stage to the roof direction is larger; The crack shape ratio and the burial depth have a great influence on the initiation life, and the initiation life accounts for the majority of the total fatigue life.