Abstract: Francis turbine runner's temperature field and stress field during welding processes are simulated,while considering thermal source;s movement along any complicated spatial route and heat loss from blade to air.The evolvement process of welding stress and the distribution of residual stress field after welding are obtained.The simulation result shows that maximal welding stress appears on the blade near the adjacent zone between blade and band or blade and crown.The invalidation reason of runner is explained,based on working stress distribution of runner.