Abstract: For a high specific speed Francis turbine, the stress and strain condition of runner blade and the internal flow characteristics were calculated and analyzed by using the method of two-way fluid solid coupling algorithm. The results show that under high rotating speed and small flow, the maximum deformation occurs at the lower position of blade tail edge and with relative large deformation at the blade tail edge centre, the stress concentrates at the blade head edge, tail edge, hub, joint position of tail edge and shroud; for other conditions, the maximum deformation of blade is at blade tail edge centre and the stress concentrates at the joint position of tail edge and hub. The blade deformation is small when the turbine runner operates normally and has little impact on the turbine internal flow field. The two-way fluid solid coupling calculation is unnecessary if only the hydraulic performance of turbine is needed to be analyzed.