Abstract: A runner stress field during welding is simulated on the basis of attaining simplified model of Francis turbine runner,realizing the thermal source loading of multi-pass welding and solving the problem of conduction between independent entities.Evolvement of longitudinal stress and residual stress field after welding are obtained.The simulation result shows that maximal welding stress appears along the adjacent area between blades and bands or blades and crown.The result can explain why fatigue crack on the turbine runner blade appears and extends.