Abstract: The welding residual tension stress is one of the main reasons which lead to the fatigue failure of francis turbine runners.The residual compressive stress improves the fatigue resistance of welding structures.The welding residual stress of runner was simulated in this paper.The result shows that there is higher residual tensile stress region in the blade outlet near the welding region.The peak value of residual tensile stress could be reduced by decreasing the length of weld bead in the outlet.The welding residual stress of runner under original and optimized welding process has been measured and analyzed.The results indicated that the residual stress could be modified and controlled by optimizing welding process.The residual tensile stress in the blade outlet near the welding region sharply decreased and turned into compressive stress.The local compressive stress of welding residual stress on francis turbine runner's easily fracturing region was realized.So the fatigue resistance of the runner efficiently increased.