Abstract: The fatigue evaluation model of laser-welded butt joint based on energy dissipation is established using the data of fatigue self-heating measured by an infrared thermal imager. The fatigue performance of the Q310NQL2-Q345NQR2 laser welded joint during the high-cycle fatigue (HCF) process is studied based on the presented model. The results show that as the stress amplitude increases, the energy dissipation of the Q310NQL2-Q345NQR2 laser welded joint increases, and when combined with the (representative volume element) RVE model to analyze, the knee point is exactly the turning point near the fatigue limit where the microstructure movement within the material gradually changes from only reversible behavior to both reversible and irreversible behaviors. The irreversible microstructure movement corresponds to the induced-damage inelastic dissipation. When the damage accumulates to a certain extent, the corresponding inelastic energy dissipation reaches a threshold value. Therefore, if taking this threshold value as the fatigue life prediction index, the HCF fatigue life prediction model of the laser-welded butt joint is well established for realizing the rapid prediction of the S-N curve.